U.S. patent number 6,277,161 [Application Number 09/406,952] was granted by the patent office on 2001-08-21 for abrasive grain, abrasive articles, and methods of making and using the same.
This patent grant is currently assigned to 3M Innovative Properties Company. Invention is credited to Darren T. Castro, Ahmet Celikkaya, Larry D. Monroe.
United States Patent |
6,277,161 |
Castro , et al. |
August 21, 2001 |
**Please see images for:
( Certificate of Correction ) ** |
Abrasive grain, abrasive articles, and methods of making and using
the same
Abstract
Alpha alumina-based abrasive grain. The abrasive grain can be
incorporated into abrasive products such as coated abrasives,
bonded abrasives, non-woven abrasives, and abrasive brushes.
Inventors: |
Castro; Darren T. (Woodbury,
MN), Celikkaya; Ahmet (Woodbury, MN), Monroe; Larry
D. (Maplewood, MN) |
Assignee: |
3M Innovative Properties
Company (St. Paul, MN)
|
Family
ID: |
23610024 |
Appl.
No.: |
09/406,952 |
Filed: |
September 28, 1999 |
Current U.S.
Class: |
51/309; 451/28;
501/128; 51/295; 51/308 |
Current CPC
Class: |
C04B
35/1115 (20130101); C09K 3/1409 (20130101); C09K
3/1418 (20130101) |
Current International
Class: |
C04B
35/111 (20060101); C09K 3/14 (20060101); B24D
003/34 (); C09K 003/14 (); C09C 001/68 () |
Field of
Search: |
;51/307,308,309,295
;501/127,128,153 ;451/28 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2014482 |
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Oct 1990 |
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CA |
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395 500 |
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Oct 1990 |
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EP |
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0 786 441 A1 |
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Jul 1997 |
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EP |
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0 603 715 B1 |
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Mar 1999 |
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EP |
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WO 95/12547 |
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May 1995 |
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WO |
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WO 97/49647 |
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Dec 1997 |
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WO |
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WO 98/12152 |
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Mar 1998 |
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WO |
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WO99/22913 |
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May 1999 |
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WO |
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WO 99/38817 |
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Aug 1999 |
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WO |
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952494 |
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Mar 1995 |
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ZA |
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Primary Examiner: Marcheschi; Michael
Attorney, Agent or Firm: Allen; Gregory D.
Claims
What is claimed is:
1. Sintered alpha alumina-based abrasive grain comprising at least
0.1 percent by weight SiO.sub.2 and in the range from 1 to 14
percent by weight ZrO.sub.2, based on the total metal oxide content
of said abrasive grain, wheren the alpha alumina of said abrasive
grain has an average crystallite size of less than 1 micrometer,
wherein said ZrO.sub.2 includes crystalline zirconia, and wherein
ZrO.sub.2 present as crystalline zirconia has an average
crystallite size of less than 0.25 micrometer.
2. The sintered alpha alumina-based abrasive grain according to
claim 1 having a density that is at least 95 percent of the
theoretical density.
3. The sintered alpha alumina-based abrasive grain according to
claim 1, wherein said Al.sub.2 O.sub.3 is present in the range from
55 to 98 percent by weight, said SiO.sub.2 is present in the range
from 1 to 3 percent by weight, and said ZrO.sub.2 is present in the
range from 1 to 14 percent by weight, based on the total metal
oxide content of said abrasive grain.
4. The sintered alpha alumina-based abrasive grain according to
claim 3, wherein at least a majority of said alpha alumina was
nucleated with a nucleating agent.
5. The sintered alpha alumina-based abrasive grain according to
claim 4, wherein said nucleating agent is .alpha.-Fe.sub.2 O.sub.3,
and is present, on a theoretical metal oxide basis, in the range
from 0.1 to 10 percent by weight, based on the total metal oxide
content of said abrasive grain.
6. The sintered alpha alumina-based abrasive grain according to
claim 1, wherein said Al.sub.2 O.sub.3 is present in the range from
70 to 93 percent by weight, said SiO.sub.2 is present in the range
from 1 to 3 percent by weight, and said ZrO.sub.2 is present in the
range from 1 to 14 percent by weight, based on the total metal
oxide content of said abrasive grain.
7. The sintered alpha alumina-based abrasive grain according to
claim 1, wherein said Al.sub.2 O.sub.3 is present in the range from
80 to 93 percent by weight, said SiO.sub.2 is present in the range
from 1 to 3 percent by weight, and said ZrO.sub.2 is present in the
range from 5 to 10 percent by weight, based on the total metal
oxide content of said abrasive grain.
8. The sintered alpha alumina-based abrasive grain according to
claim 7, wherein at least a majority of said alpha alumina was
nucleated with .alpha.-Fe.sub.2 O.sub.3 nucleating agent, and
wherein said .alpha.-Fe.sub.2 O.sub.3 nucleating agent is present,
on a theoretical metal oxide basis, in the range from 1 to 3
percent by weight, based on the metal total oxide content of said
abrasive grain.
9. The sintered alpha alumina-based abrasive grain according to
claim 1, wherein the alpha alumina of said abrasive grain has an
average crystallite size of less than 0.8 micrometer.
10. The sintered alpha alumina-based abrasive grain according to
claim 9, having a density that is at least 95 percent of the
theoretical density.
11. The sintered alpha alumina-based abrasive grain according to
claim 1, wherein the alpha alumina of said abrasive grain has an
average crystallite size of less than 0.6 micrometer.
12. The sintered alpha alumina-based abrasive grain according to
claim 1, wherein the alpha alumina of said abrasive grain has an
average crystallite size of less than 0.5 micrometer.
13. The sintered alpha alumina-based abrasive grain according to
claim 12, having a density that is at least 95 percent of the
theoretical density.
14. The sintered alpha alumina-based abrasive grain according to
claim 1, wherein the alpha alumina of said abrasive grain has an
average crystallite size of less than 0.3 micrometer.
15. The sintered alpha alumina-based abrasive grain according to
claim 1, wherein at least a majority of said alpha alumina was
nucleated with a nucleating agent.
16. The sintered alpha alumina-based abrasive grain according to
claim 15, wherein said nucleating agent is .alpha.-Fe.sub.2
O.sub.3.
17. The sintered alpha alumina-based abrasive grain according to
claim 1, further comprising metal oxide selected from the group
consisting of: lithium oxide, manganese oxide, chromium oxide,
praseodymium oxide, dysprosium oxide, samarium oxide, cobalt oxide,
zinc oxide, neodymium oxide, yttrium oxide, ytterbium oxide,
magnesium oxide, nickel oxide, sodium oxide, titanium oxide,
lanthanum oxide, gadolinium oxide, dysprosium oxide, europium
oxide, ferric oxide, hafnium oxide, erbium oxide, and combinations
thereof.
18. The sintered alpha alumina-based abrasive grain according to
claim 1, which comprises in the range from 1 to 3 percent by weight
of said SiO.sub.2, based on the total metal oxide content of said
abrasive grain.
19. The sintered alpha alumina-based abrasive grain according to
claim 1, which comprises in the range from 4 to 14 percent by
weight of said ZrO.sub.2, based on the total metal oxide content of
said abrasive grain.
20. The sintered alpha alumina-based abrasive grain according to
claim 1, which comprises in the range from 1 to 3 percent by weight
of said SiO.sub.2 and in the range from 4 to 14 percent by weight
of said ZrO.sub.2, based on the total metal oxide ontent of said
abrasive grain.
21. An abrasive article including:
a binder; and
a plurality of abrasive grain according to claim 1 secured within
said article by said binder.
22. The abrasive article according to claim 21 wherein said
abrasive article is a grinding wheel.
23. A coated abrasive article comprising:
a backing having a major surface; and
an abrasive layer comprising said plurality of abrasive grain
according to claim 1 secured to said major surface of said backing
by a binder.
24. A method for making alpha alumina-based ceramic abrasive grain,
said method comprising:
preparing a dispersion by combining components comprising liquid
medium, peptizing agent, zirconia source, silica source, and
alumina source;
converting said dispersion to particulate alpha alumina-based
ceramic abrasive grain precursor material; and
sintering said precursor material to provide sintered alpha
alumina-based abrasive grain comprising at least 0.1 percent by
weight SiO.sub.2 and in the range from 1 to 14 percent by weight
ZrO.sub.2, based on the total metal oxide content of said abrasive
grain, wherein the alpha alumina of said abrasive grain has an
average crystallite size of less than 1 micrometer, wherein said
ZrO.sub.2 includes crystalline zirconia, and wherein ZrO.sub.2
present as crystalline zirconia has an average crystallite size of
less than 0.25 micrometer.
25. The method according to claim 24, wherein said alumina source
is boehmite.
26. The method according to claim 25, wherein between said
converting and said sintering, said method further comprises (i)
impregnating said precursor material with a mixture prepared by
combining components comprising a second liquid medium and at least
one of metal oxide or metal oxide precursor to provide impregnated
precursor material; (ii) drying said impregnated precursor
material; and (iii) calcining the dried, impregnated precursor
material.
27. The method according to claim 25, wherein said sintering
conducted below 1400.degree. C.
28. The method according to claim 27, wherein said sintered alpha
alumina-based abrasive grain has a density that is at least 95
percent of the theoretical density.
29. The method according to claim 27, wherein said zirconia source
includes zirconium salt.
30. The method according to claim 27, wherein said zirconia source
includes zirconia sol.
31. The method according to claim 25, wherein said silica source
includes silica sol.
32. The method according to claim 25, wherein said components for
preparing said dispersion further comprise nucleating material, and
wherein at least a majority of the alpha alumina of said abrasive
grain was nucleated with a nucleating agent.
33. The method according to claim 25, wherein sintered alpha
alumina-based abrasive grain comprises in the range from 1 to 3
percent by weight of said SiO.sub.2, based on the total metal oxide
content of said abrasive grain.
34. The method according to claim 25, wherein sintered alpha
alumina-based abrasive grain comprises in the range from 4 to 14
percent by weight of said ZrO.sub.2, based on the total metal oxide
content of said abrasive grain.
35. The method according to claim 27, wherein sintered alpha
alumina-based abrasive grain comprises in the range from 1 to 3
percent by weight of said SiO.sub.2 and in the range from 4 to 14
percent by weight of said ZrO.sub.2, based on the total metal oxide
content of said abrasive grain.
36. A method for making an abrasive article, said method
comprising:
preparing a dispersion by combining components comprising liquid
medium, peptizing agent, zirconia source, silica source, and
alumina source;
converting said dispersion to particulate alpha alumina-based
ceramic abrasive grain precursor material;
sintering said precursor material to provide sintered alpha
alumina-based abrasive grain comprising at least 0.1 percent by
weight SiO.sub.2 and in the range from 1 to 14 percent by weight
ZrO.sub.2, based on the total metal oxide content of said abrasive
grain, wherein the alpha alumina of said abrasive grain has an
average crystallite size of less than 1 micrometer, wherein said
ZrO.sub.2 includes crystalline zirconia, and wherein ZrO.sub.2
present as crystalline zirconia has an average crystallite size of
less than 0.25 micrometer; and
combining at least a plurality of said alpha alumina-based ceramic
abrasive grain with binder to provide an abrasive article.
37. The method according to claim 36, wherein said alumina source
is boehmite.
38. The method according to claim 37, wherein said abrasive article
is a coated abrasive article that includes a backing.
39. The method according to claim 37, wherein combining at least a
plurality of said alpha alumina-based ceramic abrasive grain with
binder includes combining fused alumina abrasive grain with said
binder.
40. The method according to claim 37, wherein sintered alpha
alumina-based abrasive grain comprises in the range from 1 to 3
percent by weight of said SiO.sub.2 and in the range from 4 to 14
percent by weight of said ZrO.sub.2, based on the total metal oxide
content of said abrasive grain.
41. A method for making alpha a lumina-based ceramic abrasive
grain, said method comprising:
preparing a dispersion by combining components comprising first
liquid medium, peptizing agent, silica source, and alumina
source;
converting said dispersion to particulate alpha alumina-based
ceramic abrasive grain precursor material;
impregnating said precursor material with a composition comprising
a mixture comprising a second liquid medium and a zirconia source;
and
sintering the impregnated precursor material to provide sintered
alpha alumina-based abrasive grain comprising at least 0.1 percent
by weight SiO.sub.2 and in the range from 1 to 14 percent by weight
ZrO.sub.2, based on the total metal oxide content of said abrasive
grain, wherein the alpha alumina of said abrasive grain has an
average crystallite size of less than 1 micrometer, wherein said
ZrO.sub.2 includes crystalline zirconia, and wherein ZrO.sub.2
present as crystalline zirconia has an average crystallite size of
less than 0.25 micrometer.
42. The method according to claim 41, wherein said alumina source
is boehmite.
43. The method according to claim 42, wherein the components
combined for said dispersion further comprise a zirconia
source.
44. The method according to claim 43, wherein said zirconia source
includes zirconia sol.
45. The method according to claim 42, wherein said sintering
conducted below 1400.degree. C.
46. The method according to claim 45 wherein said sintered alpha
alumina-based abrasive grain has a density that is at least 95
percent of the theoretical density.
47. The method according to claim 42, wherein said zirconia source
includes zirconium salt.
48. The method according to claim 42, wherein said silica source
includes silica sol.
49. The method according to claim 42, wherein said components for
preparing said dispersion further comprise nucleating material, and
wherein at least a majority of the alpha alumina of said abrasive
grain was nucleated with a nucleating agent.
50. The method according to claim 42, wherein sintered alpha
alumina-based abrasive grain comprises in the range from 1 to 3
percent by weight of said SiO.sub.2, based on the total metal oxide
content of said abrasive grain.
51. The method according to claim 42, wherein sintered alpha
alumina-based abrasive grain comprises in the range from 4 to 14
percent by weight of said ZrO.sub.2, based on the total metal oxide
content of said abrasive grain.
52. The method according to claim 42, wherein sintered alpha
alumina-based abrasive grain comprises in the range from 1 to 3
percent by weight of said SiO.sub.2 and in the range from 4 to 14
percent by weight of said ZrO.sub.2, based on the total metal oxide
content of said abrasive grain.
53. A method for making an abrasive article, said method
comprising:
preparing a dispersion by combining components comprising first
liquid medium, peptizing agent, silica source, and alumina
source;
converting said dispersion to particulate alpha alumina-based
ceramic abrasive grain precursor material;
impregnating said precursor material with a composition comprising
a mixture comprising a second liquid medium and a zirconia
source;
sintering the impregnated precursor material to provide sintered
alpha alumina-based abrasive grain comprising at least 0.1 percent
by weight SiO.sub.2 and in the range from 1 to 14 percent by weight
ZrO.sub.2, based on the total metal oxide content of said abrasive
grain, wherein the alpha alumina of said abrasive grain has an
average crystallite size of less than 1 micrometer, wherein said
ZrO.sub.2 includes crystalline zirconia, and wherein ZrO.sub.2
present as crystalline zirconia has an average crystallite size of
less than 0.25 micrometer; and
combining at least a plurality of said alpha alumina-based ceramic
abrasive grain with binder to provide an abrasive article.
54. The method according to claim 53, wherein said alumina source
is boehmite.
55. The method according to claim 54, wherein said abrasive article
is a coated abrasive article that includes a backing.
56. The method according to claim 55, wherein combining at least a
plurality of said alpha alumina-based ceramic abrasive grain with
binder includes combining fused alumina abrasive grain with said
binder.
57. The method according to claim 54, wherein said components for
preparing said dispersion further comprise nucleating material, and
wherein at least a majority of the alpha alumina of said abrasive
grain was nucleated with a nucleating agent.
58. The method according to claim 54, wherein sintered alpha
alumina-based abrasive grain comprises in the range from 1 to 3
percent by weight of said SiO.sub.2 and in the range from 4 to 14
percent by weight of said ZrO.sub.2, based on the total metal oxide
content of said abrasive grain.
59. A method of abrading a surface comprising:
contacting a plurality of abrasive grain with a surface of a
substrate at a contact pressure of at least 1 kg/cm.sup.2, wherein
at least a portion of said abrasive grain is sintered alpha
alumina-based abrasive grain comprising at least 0.1 percent by
weight SiO.sub.2 and in the range from 1 to 14 percent by weight
ZrO.sub.2, based on the total metal oxide content of said abrasive
grain, wherein the alpha alumina of said abrasive grain has an
average crystallite size of less than 1 micrometer, wherein said
ZrO.sub.2 includes crystalline zirconia, and wherein ZrO.sub.2
present as crystalline zirconia has an average crystallite size of
less than 0.25 micrometer; and
moving at least of one said plurality of abrasive grain or said
surface relative to the other to abrade at least a portion of said
surface with said abrasive grain.
60. The method according to claim 59 wherein at least 75 percent by
weight of the abrasive grain is said sintered alpha alumina-based
abrasive grain.
61. The method according to claim 59 wherein sintered alpha
alumina-based abrasive grain comprises in the range from 1 to 3
percent by weight of said SiO.sub.2, based on the total metal oxide
content of said abrasive grain.
62. The method according to claim 59 wherein sintered alpha
alumina-based abrasive grain comprises in the range from 4 to 14
percent by weight of said ZrO.sub.2, based on the total metal oxide
content of said abrasive grain.
63. The method according to claim 59 wherein sintered alpha
alumina-based abrasive grain comprises in the range from 1 to 3
percent by weight of said SiO.sub.2 and in the range from 4 to 14
percent by weight of said ZrO.sub.2, based on the total metal oxide
content of said abrasive grain.
64. The method according to claim 59 wherein said contact pressure
of at least 3.5 kg/cm.sup.2.
65. The method according to claim 59 wherein said substrate is 1018
mild steel.
66. The method according to claim 59 wherein said contact pressure
of at least 5 kg/cm.sup.2.
67. The method according to claim 59 wherein said contact pressure
of at least 7 kg/cm.sup.2.
68. The method according to claim 59 wherein said contact pressure
of at least 10 kg/cm.sup.2.
69. The method according to claim 59 wherein said contact pressure
of at least 20 kg/cm.sup.2.
70. The method according to claim 59 wherein said substrate is
selected from the group consisting of carbon steel stainless steel,
titanium, paint, wood, and plastic.
71. The method according to claim 59 wherein said substrate is 4140
steel.
72. The method according to claim 59 wherein said substrate is 4150
steel.
Description
FIELD OF THE INVENTION
This invention pertains to abrasive grain and a method of making
abrasive grain. The abrasive grain can be incorporated into a
variety of abrasive articles, including bonded abrasives, coated
abrasives, nonwoven abrasives, and abrasive brushes.
DESCRIPTION OF RELATED ART
In the early 1980's a new and substantially improved type of
alumina abrasive grain, commonly referred to as "sol gel" or "sol
gel-derived" abrasive grain, was commercialized. This new type of
alpha alumina abrasive grain had a microstructure made up of very
fine alpha alumina crystallites. The grinding performance of the
new abrasive grain on metal, as measured, for example, by life of
abrasive products made with the grain was dramatically longer than
such products made from conventional, fused alumina abrasive
grain.
In general, sol gel abrasive grain are typically made by preparing
a dispersion or sol comprising water, alumina monohydrate
(boehmite), and optionally peptizing agent (e.g., an acid such as
nitric acid), gelling the dispersion, drying the gelled dispersion,
crushing the dried dispersion into particles, calcining the
particles to remove volatiles, and sintering the calcined particles
at a temperature below the melting point of alumina. Frequently,
the dispersion also includes one or more oxide modifiers (e.g.,
CeO.sub.2, Cr.sub.2 O.sub.3, CoO, Dy.sub.2 O.sub.3, Er.sub.2
O.sub.3, Eu.sub.2 O.sub.3, Fe.sub.2 O.sub.3, Gd.sub.2 O.sub.3,
HfO.sub.2, La.sub.2 O.sub.3, Li.sub.2 O, MgO, MnO, Na.sub.2 O,
Nd.sub.2 O.sub.3, NiO, Pr.sub.2 O.sub.3, Sm.sub.2 O.sub.3,
SiO.sub.2, SnO.sub.2, TiO.sub.2, Y.sub.2 O.sub.3, Yb.sub.2 O.sub.3,
ZnO, and ZrO.sub.2), nucleating agents (e.g., .alpha.-Al.sub.2
O.sub.3, .alpha.-Cr.sub.2 O.sub.3, and .alpha.-Fe.sub.2 O.sub.3)
and/or precursors thereof. Such additions are typically made to
alter or otherwise modify the physical properties and/or
microstructure of the sintered abrasive grain. In addition, or
alternatively, such oxide modifiers, nucleating agents, and/or
precursors thereof may be impregnated into the dried or calcined
material (typically calcined particles). Further details regarding
sol gel abrasive grain, including methods for making them, can be
found, for example, in U.S. Pat. No. 4,314,827 (Leitheiser et al.),
U.S. Pat. No. 4,518,397 (Leitheiser et al.), U.S. Pat. No.
4,623,364 (Cottringer et al.), U.S. Pat. No. 4,744,802 (Schwabel),
U.S. Pat. No. 4,770,671 (Monroe et al.), U.S. Pat. No. 4,881,951
(Wood et al.), U.S. Pat. No. 4,960,441 (Pellow et al.) U.S. Pat.
No. 5,011,508 (Wald et al.), U.S. Pat. No. 5,090,968 (Pellow), U.S.
Pat. No. 5,139,978 (Wood), U.S. Pat. No. 5,201,916 (Berg et al.),
U.S. Pat. No. 5,227,104 (Bauer), U.S. Pat. No. 5,366,523
(Rowenhorst et al.), U.S. Pat. No. 5,429,647 (Larmie), U.S. Pat.
No. 5,547,479 (Conwell et al.), U.S. Pat. No. 5,498,269 (Larmie),
U.S. Pat. No. 5,551,963 (Larmie), U.S. Pat. No. 5,725,162 (Garg et
al.), and U.S. Pat. No. 5,776,214 (Wood).
Over the past fifteen years sintered alumina abrasive grain, in
particular sol gel-derived alpha alumina-based sintered abrasive
grain, have been used in a wide variety of abrasive products (e.g.,
bonded abrasives, coated abrasives, and abrasive brushes) and
abrading applications, including both low and high pressure
grinding applications. For example sol gel-derived abrasive grain
have been incorporated into resin bonded grinding wheels, and have
been found to be particularly useful in high pressure, high stock
removal grinding applications. Such abrasive grain have been used
in vitrified grinding wheels for the precision grinding of
camshafts. Sol gel-derived abrasive grain have also been
incorporated into medium grade coated abrasive products that are
used to sand wood cabinet panels. In addition, coated abrasive
discs that include sol gel-derived abrasive grain are used under
relatively light pressure to abrade painted automotive parts.
For some higher pressure grinding applications, it is preferred
that the sintered alumina abrasive grain be relatively tough to
withstand the high grinding forces. Such increased toughness may be
achieved through the addition of various metal oxides to the
alumina crystal structure. Alternatively, in some lower pressure
grinding applications, it is preferred that the sintered alumina
abrasive grain be more friable so that the abrasive grain can
"breakdown" during grinding. In order to achieve the optimum
grinding performance under these wide ranges of grinding
conditions, a variety of sintered alpha alumina abrasive grains
have been developed and commercialized.
Although there are a number of commercially available sintered
alumina abrasive grains, sintered alumina abrasive grain that can
provide desirable grinding or abrading characteristics (e.g., long
life, high metal removal rates, and desired finish) under certain
grinding conditions (e.g., under relatively high grinding pressure
or relatively low grinding pressures) what is desired is an
abrasive grain that has desirable grinding or abrading
characteristics under a relatively wide range of grinding pressure
(e.g., both high and low grinding pressures). The availability of
such an abrasive grain is advantageous, for example, because it
reduces, or perhaps in some cases, eliminates the need for multiple
inventories of abrasive grain or abrasive products. Further, for
example, the availability of abrasive products incorporating such
an abrasive grain reduces or eliminates the need for the end user
to change the abrasive product because of a change in grinding
conditions.
SUMMARY OF THE INVENTION
In one aspect, the present invention surprisingly provides sintered
alpha alumina-based abrasive grain comprising SiO.sub.2 and
ZrO.sub.2 (typically at least 0.1 percent (preferably, at least
0.2, 0.25, 0.3, or even 0.5 percent) by weight of each of SiO.sub.2
and ZrO.sub.2, based on the total metal oxide content of the
abrasive grain), wherein the alpha alumina of the abrasive grain
has an average crystallite size of less than 1 (preferably, less
than 0.8, 0.7 0.6, 0.5, 0.4, or even 0.3) micrometer, and wherein
the ZrO.sub.2 that is present as crystalline zirconia has an
average crystallite size of less than 0.25 micrometer. Typically,
at least a majority of the alpha alumina was nucleated with a
nucleating agent. Preferably the average crystallite size of the
alpha alumina is less than 0.75 micrometer, more preferably, less
than 0.5 micrometer, and even more preferably, less than 0.3
micrometer.
One preferred sintered alpha alumina-based abrasive grain according
to the present invention comprises at least 0.1 percent
(preferably, at least 0.2, 0.25, 0.3, or even 0.5 percent; more
preferably at least 1 percent; even more preferably in the range
from 1 to 3 percent) by weight SiO.sub.2 and at least 0.1 percent
(preferably, at least 0.2, 0.25, 0.3, or even 0.5 percent; more
preferably at least 1 percent; even more preferably in the range
from 1 to 14 percent, or even from 4 to 14 percent) by weight
ZrO.sub.2, based on the total metal oxide content of the abrasive
grain), wherein the alpha alumina of the abrasive grain has an
average crystallite size of less than 1 micrometer, and wherein the
ZrO.sub.2 that is present as crystalline zirconia has an average
crystallite size of less than 0.25 micrometer.
In another aspect, the present invention provides a method of
abrading a surface, the method comprising:
contacting a plurality of abrasive grain with a surface (e.g., a
surface of a substrate (e.g., a titanium substrate or a steel
substrate such as carbon steel (e.g., a 1018 mild steel substrate),
a stainless steel (e.g., 304 stainless steel) substrate, or a tool
steel (e.g., 4140 steel and 4150 steel) substrate) at a contact
pressure of at least 1 kg/cm.sup.2, in some cases, preferably, 2
kg/cm.sup.2, 3.5 kg/cm.sup.2, 5 kg/cm.sup.2, 7 kg/cm.sup.2, 10
kg/cm.sup.2, 15 kg/cm.sup.2, and 20 kg/cm.sup.2, wherein at least a
portion of the abrasive grain is alpha alumina-based abrasive grain
according to the present invention; and
moving at least of one the plurality of abrasive grain or the
surface relative to the other to abrade at least a portion of the
surface with the abrasive grain. Preferably, at least 75 percent
(or even 100 percent) by weight of the abrasive grain is abrasive
grain according to the present invention. Examples of other
substrate surfaces that can be abraded include paint, wood, and
plastic.
Although not wanting to be bound by theory, it is believed that the
presence of the Al.sub.2 O.sub.3, SiO.sub.2, and ZrO.sub.2 and the
crystallite size of the Al.sub.2 O.sub.3 and ZrO.sub.2 have a
significant affect on its grinding performance. The small alpha
alumina crystals are believed to result in a fast cutting, long
lasting abrasive. The presence of zirconia and silica, are believed
to aid in the densification of the alpha alumina and in minimizing
the growth of the desirably small alpha alumina crystals, resulting
in an abrasive grain that works well at higher pressures. In
addition, it is believed that the presence of the zirconia may
toughen the abrasive grain.
In another aspect, the present invention provides a method for
making alpha alumina-based ceramic abrasive grain, the method
comprising:
preparing a mixture (e.g., a dispersion) by combining components
comprising liquid medium, zirconia source (e.g., a zirconia sol or
a salt such as zirconyl acetate), silica source (e.g., a silica
sol), and alumina source (preferably, boehmite);
converting the mixture to particulate alpha alumina-based ceramic
abrasive grain precursor material; and
sintering the precursor material to provide sintered alpha
alumina-based abrasive grain according to the present invention. If
the alumina source comprises particulate such as boehmite, alpha
alumina powder, or gamma alumina powder, the components used to
prepare the dispersion also include peptizing agent (e.g., an acid
such as nitric acid).
In another aspect, the present invention provides a method for
making alpha alumina-based ceramic abrasive grain, the method
comprising:
preparing a mixture (e.g., a dispersion) by combining components
comprising first liquid medium, silica source, alumina source
(e.g., boehmite), and optionally zirconia source;
converting the mixture to particulate alpha alumina-based ceramic
abrasive grain precursor material;
impregnating the precursor material with a composition comprising a
mixture comprising a second liquid medium and a zirconia source;
and
sintering the impregnated precursor material to provide sintered
alpha alumina-based abrasive grain according to the present
invention. If the alumina source used in preparing the initial
dispersion comprises particulate such as boehmite, alpha alumina
powder, or gamma alumina powder, the dispersion also includes a
peptizing agent (e.g., an acid such as nitric acid). Zirconia
source for the initial mixture and the impregnating composition can
be the same or different. Optionally, the impregnating composition
further comprises other (i.e., other than a zirconia source) metal
oxide source.
In this application:
"Boehmite" refers to alpha alumina monohydrate and boehmite
commonly referred to in the art as "pseudo" boehmite (i.e.,
Al.sub.2 O.sub.3.xH.sub.2 O, wherein x=1 to 2).
"Abrasive grain precursor" or "unsintered abrasive grain" refers to
a dried alumina-based dispersion (i.e., "dried abrasive grain
precursor") or a calcined alumina-based dispersion (i.e., "calcined
abrasive grain precursor"), typically in the form of particles,
that has a density of less than 80% (typically less than 60%) of
theoretical, and is capable of being sintered or impregnated with
an impregnation composition and then sintered to provide alpha
alumina-based ceramic abrasive grain. "Alpha alumina-based ceramic
abrasive" as used herein refers to a sintered abrasive grain that
has been sintered to a density of at least 85% (preferably, at
least 90% and more preferably, at least 95%) of theoretical, and
contains, on a theoretical oxide basis, at least 60% by weight
Al.sub.2 O.sub.3, wherein at least 50% by weight of the total
amount of alumina is present as alpha alumina.
"Nucleating material" refers to material that enhances the
transformation of transitional alumina(s) to alpha alumina via
extrinsic nucleation. The nucleating material can be a nucleating
agent (i.e., material having the same or approximately the same
crystalline structure as alpha alumina, or otherwise behaving as
alpha alumina) itself (e.g., alpha alumina seeds, alpha Fe.sub.2
O.sub.3 seeds, or alpha Cr.sub.2 O.sub.3 seeds) or a precursor
thereof. Other nucleating agents may include Ti.sub.2 O.sub.3
(having a trigonal crystal structure), MnO.sub.2 (having a rhombic
crystal structure), Li.sub.2 O (having a cubic crystal structure),
and titanates (e.g., magnesium titanate and nickel titanate).
"Dispersion" or "sol" refers to a solid-in-liquid two-phase system
wherein one phase comprises finely divided particles (in the
colloidal size range) distributed throughout a liquid. A "stable
dispersion" or "stable sol" refer to a dispersion or sol from which
the solids do not appear by visual inspection to begin to gel,
separate, or settle upon standing undisturbed for about 2
hours.
"Impregnation composition" refers to a solution or dispersion of a
liquid medium, and a source of metal oxide that can be impregnated
into an abrasive grain precursor. "Impregnated abrasive grain
precursor" refers to a dried alumina-based dispersion (i.e.,
"impregnated dried abrasive grain precursor") or a calcined
alumina-based dispersion (i.e., "impregnated calcined abrasive
grain precursor") that has a density of less than 80% (typically
less than 60%) of theoretical, and has been impregnated with an
impregnation composition, and includes impregnated dried particles
and impregnated calcined particles.
"Sintering" refers to a process of heating at a temperature below
the melting temperature of the material being heated to provide
densification and crystallite growth to provide a tough, hard, and
chemically resistant ceramic material. The alpha alumina-based
ceramic abrasive grain according to the present invention is not
made by a fusion process wherein heating is carried out at a
temperature above the melting temperature of the material being
heated.
Typically, abrasive grain according to the present invention
exhibit good grinding efficiencies under both relatively high and
low pressure grinding conditions. Although not wanting to be bound
by theory, it is believed that the use of nucleating material
facilitates in obtaining alpha alumina crystals that are less than
one micrometer in size. Further, it is believed that the presence
of zirconia tends to assist in the densification and "toughening"
of the alumina crystal matrix, thereby allowing the resulting
abrasive grain being able to withstand the higher grinding forces.
It is also believed that the addition of silica aids in the
sintering process.
Abrasive grain according to the present invention can be
incorporated into various abrasive articles such as coated
abrasives, bonded abrasives (including vitrified and resinoid
grinding wheels), nonwoven abrasives, and abrasive brushes. The
abrasive articles typically comprise abrasive grain according to
the present invention and binder.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a fragmentary cross-sectional schematic view of a coated
abrasive article including abrasive grain made according to the
method of the present invention;
FIG. 2 is a perspective view of a bonded abrasive article including
abrasive grain made according to the method of the present
invention;
FIG. 3 is an enlarged schematic view of a nonwoven abrasive article
including abrasive grain made according to the method of the
present invention;
FIGS. 4 and 6 are elevational plan views of an extruder useful in
the methods according to the present invention, while
FIG. 5 is an enlarged top plan of the extruder feed port;
FIG. 7 is a scanning electron photomicrograph of a fracture surface
of an abrasive grain according to the present invention; and
FIG. 8 is a back scattered electron photomicrograph of abrasive
grain according to the present invention.
DETAILED DESCRIPTION
Preferably, the alumina source used to prepare the initial mixture
is boehmite. Other suitable alumina sources that are capable of
providing alpha alumina crystals during the sintering portion of
the process include alpha alumina powders, gamma alumina powders,
aluminum formoacetate, aluminum nitroformoacetate, and aluminum
salts.
More specific examples of suitable aluminum compounds which can be
used as alumina precursors include basic aluminum carboxylates,
basic aluminum nitrates, partially hydrolyzed aluminum alkoxides or
other aluminum salts and complexes. Preferred basic aluminum salts
include those with carboxylate or nitrate counterions or mixtures
of these salts. In the case of the basic aluminum carboxylates,
these are of the general formula Al(OH).sub.y
(carboxylate).sub.3-y, where y is between 1 and 2, preferably
between 1 and 1.5, and the carboxylate counterion is selected from
the group consisting of formate, acetate, propionate, and oxalate
or combinations of these carboxylates. These materials can be
prepared by digesting aluminum metal in a solution of the
carboxylic acid as described in U.S. Pat. No. 3,957,598, the
disclosure of which is incorporated herein by reference. The basic
aluminum nitrates can also be prepared by digesting aluminum metal
in a nitric acid solution as described in U.S. Pat. No. 3,340,205
or British patent 1,193,258, or by the thermal decomposition of
aluminum nitrate as described in U.S. Pat. No. 2,127,504, the
disclosures of which are incorporated herein by reference. These
materials can also be prepared by partially neutralizing an
aluminum salt with a base. The basic aluminum nitrates have the
general formula Al(OH).sub.z (NO.sub.3).sub.3-z, where z is between
about 0.5 to 2.5.
Suitable boehmites include those commercially available under the
trade designation "HIQ" (e.g., "HIQ-10," "HIQ-20," "HIQ-30," and
"HIQ-40") from Alcoa Industrial Chemicals, and those commercially
available under the trade designations of "DISPERAL" from Condea
GmbH, Hamburg, Germany, and "DISPAL 23N480" and "CATAPAL D" from
Condea Vista Company, Houston, Tex. These boehmites or alumina
monohydrates are in the alpha form, and include relatively little,
if any, hydrated phases other than monohydrates (although very
small amounts of trihydrate impurities can be present in some
commercial grade boehmite, which can be tolerated). They have a low
solubility in water and have a high surface area (typically at
least about 180 m.sup.2 /g). Preferably the dispersed boehmite used
to make abrasive grain according to the present invention has an
average crystallite size of less than about 20 nanometers (more
preferably, less than 12 nanometers). In this context, "crystallite
size" is determined by the 120 and 031 x-ray reflections.
The preferred liquid medium is typically water, although organic
solvents, such as lower alcohols (typically C.sub.1-6 alcohols),
hexane, or heptane, may also be useful as the liquid medium. The
water may be tap water, distilled water or deionized water. In some
instances, it is preferable to heat the liquid medium (e.g., ls
water) at (e.g., 30-70.degree. C.) to improve the dispersibility of
the boehmite, or other particulate material.
The dispersion may further comprise peptizing agents; these
peptizing agents are generally soluble ionic compounds which are
believed to cause the surface of a particle or colloid to be
uniformly charged in a liquid medium (e.g., water). The preferred
peptizing agents are acids or acid compounds. Examples of typical
acids include monoprotic acids and acid compounds, such as acetic,
hydrochloric, formic, and nitric acid, with nitric acid being
preferred. The amount of acid used depends, for example, on the
dispersibility of the particulate alumina source, the percent
solids of the dispersion, the components of the dispersion, the
amounts, or relative amounts of the components of the dispersion,
the particle sizes of the components of the dispersion, and/or the
particle size distribution of the components of the dispersion. For
boehmite, the dispersion typically contains at least, 0.1 to 20%,
preferably 1% to 10% by weight acid, and most preferably 3 to 8% by
weight acid, based on the weight of boehmite in the dispersion.
In some instances, the acid may be applied to the surface of the
boehmite particles prior to being combined with the water. The acid
surface treatment may provide improved dispersibility of the
boehmite in the water.
The silica source is preferably added to the alumina dispersion as
a colloidal sol. The colloidal silica comprises finely divided
particles of amorphous or crystalline silica typically having one
or more of their dimensions within a range of about 3 nanometers to
about 1 micrometer. The average silica particle size in the
colloidal is preferably less than about 150 nanometers, more
preferably less than about 100 nanometers, and most preferably less
than about 50 nanometers. In most instances, the silica particles
can be on the order of about 3-15 nanometers. In most instances,
the colloidal silica comprises a distribution or range of metal
oxide particle sizes. Silica sols are available, for example, from
Nalco of Naperville, Ill.; and Eka Nobel of Augusta, Ga. Silica
sols include those available under the trade designations "NALCO
1115," "NALCO 1130," "NALCO 2326," "NALCO 1034A," and "NALCOAG
1056" from Nalco Products, Inc. of Naperville, Ill., wherein the
latter two are examples of acidic silica sols; and "NYACOL 215"
from Eka Nobel, Inc. For additional information on silica sols see,
for example, U.S. Pat. No. 5,611,829 (Monroe et al.) and U.S. Pat.
No. 5,645,619 (Erickson et al.), the disclosures of which are
incorporated herein by reference.
It is preferred to include a nucleating material or agent in the
boehmite dispersion. One preferred nucleating material for
practicing the present invention includes iron oxide or an iron
oxide precursor. Sources of iron oxide, which in some cases may act
as or provide a material that acts as a nucleating material,
include hematite (i.e., .alpha.-Fe.sub.2 O.sub.3), as well as
precursors thereof (i.e., goethite (.alpha.-FeOOH), lepidocrocite
(.gamma.-FeOOH), magnetite (Fe.sub.3 O.sub.4), and maghemite
(.gamma.-Fe.sub.2 O.sub.3)). Suitable precursors of iron oxide
include iron-containing material that, when heated, will convert to
.alpha.-Fe.sub.2 O.sub.3. For additional details regarding the
addition of iron sources to the dispersion or ceramic precursor
material see, for example, U.S. Pat. No. 5,611,829 (Monroe et al.)
and U.S. Pat. No. 5,645,619 (Erickson et al.), the disclosures of
which are incorporated herein by reference.
Other suitable nucleating materials may include .alpha.-Cr.sub.2
O.sub.3 precursors such as chromium nitrate
(Cr(NO.sub.3).sub.3.9H.sub.2 O) and chromium acetate; MnO.sub.2
precursors such as manganese nitrate (Mn(NO.sub.3).sub.2.4H.sub.2
O), manganese acetate, and manganese formate; and Li.sub.2 O
precursors such as lithium nitrate (LiNO.sub.3), lithium acetate,
and lithium formate. Additional details regarding nucleating
materials are also disclosed, for example, in U.S. Pat. No.
4,623,364 (Cottringer et al.), U.S. Pat. No. 4,744,802 (Schwabel),
U.S. Pat. No. 4,964,883 (Morris et al.), U.S. Pat. No. 5,139,978
(Wood), and U.S. Pat. No. 5,219,806 (Wood), the disclosures of
which are incorporated herein by reference.
Suitable zirconia sources include zirconium salts and zirconia
sols, although the zirconia source in an impregnation composition
is typically a zirconium salt that forms a solution in the liquid
medium. Examples of zirconium salts include zirconyl acetate
(ZrO(CH.sub.3 COO).sub.2), zirconium oxynitrate
(ZrO(NO.sub.3).sub.2.xH.sub.2 O), zirconium hydroxynitrate,
zirconium formate, and zirconium acetylacetonate, zirconium
alkoxides (butoxide, ethoxide, propoxide, tert-butoxide), zirconium
chloride, zirconium nitrate, ammonium complex, zirconium
tetrachloride, zirconium oxychloride octahydrate. The zirconia sol
comprises finely divided particles of amorphous or crystalline
zirconia typically having one or more of their dimensions
preferably within a range of about 3 nanometers to about 250
nanometers. The average zirconia particle size in the colloidal
zirconia is preferably less than about 150 nanometers, more
preferably less than about 100 nanometers, and most preferably less
than about 50 nanometers. In some instances, the zirconia particles
can be on the order of about 3-10 nanometers. In most instances,
the colloidal zirconia comprises a distribution or range of
zirconia particle sizes. Zirconia sols include those available from
Nyacol Products, Inc., Ashland, Mass. under the trade designations
"ZR10/20" and "ZR100/20". For more information on zirconia sols,
see, for example, U.S. Pat. Nos. 5,498,269 (Larmie) and U.S. Pat.
No. 5,551,963 (Larmie), the disclosures of which are incorporated
herein by reference.
The amount of the alumina source, silica source, nucleating
material, and zirconia source in the initial dispersion, and/or
provided by the impregnation composition, is selected to provide
the desired weight percentages in the sintered abrasive grain.
Typically, abrasive grain according to the present invention
comprise, on a theoretical metal oxide basis, about 55 to about 99
percent by weight (preferably, about 65 to 95 percent by weight;
more preferably, about 70 to about 93 percent by weight; and even
more preferably about 80 to 93 percent by weight) Al.sub.2 O.sub.3,
about 0.1 to about 10 percent by weight (preferably, about 0.5 to
about 5 percent by weight; more preferably, about 0.75 to about 3
percent by weight; and even more preferably, about 1 to about 2
percent by weight) SiO.sub.2, and about 0.5 to about 15 percent by
weight (preferably, about 1 to about 13; more preferably, about 3
to about 10 percent by weight, and even more preferably, about 5 to
about 10 percent by weight) ZrO.sub.2, based on the total metal
oxide content of the abrasive grain. Further the abrasive grain
typically comprises, on theoretical metal oxide basis, about 0.1 to
about 10 (preferably, about 0.5 to about 10 percent by weight; more
preferably, about 0.75 to about 5; and even more preferably, about
1 to about 3 percent by weight) nucleating agent, based on the
total metal oxide content of the abrasive grain.
The initial mixture may further comprise other metal oxide sources
(i.e., materials that are capable of being converting into metal
oxide with the appropriate heating conditions), sometimes referred
to as a metal oxide modifiers. Such metal oxide modifiers may alter
the physical properties and/or chemical properties of the resulting
abrasive grain. The amount of these other metal oxides incorporated
into the initial mixture and/or impregnation composition may
depend, for example, on the desired composition and/or properties
of the sintered abrasive grain, as well as on the effect or role
the additive may have on or play in the process used to make the
abrasive grain.
The other metal oxides may be added to the initial mixture as a
metal oxide (e.g., a colloidal suspension or a sol) and/or as a
precursor (e.g., a metal salt such as metal nitrate salts, metal
acetate salts, metal citrate salts, metal formate salts, and metal
chloride salts). For metal oxide particles, it is generally
preferred that the metal oxide particles are generally less than 5
micrometers, preferably less than 1 micrometer in size. The
colloidal metal oxides are discrete finely divided particles of
amorphous or crystalline metal oxide typically having one or more
of their dimensions within a range of about 3 nanometers to about 1
micrometer. Preferably, the "colloidal metal oxide sols" are a
stable (i.e., the metal oxide solids in the sol or dispersion do
not appear by visual inspection to begin to gel, separate, or
settle upon standing undisturbed for about 2 hours) suspension of
colloidal particles (preferably in a liquid medium having a pH of
less than 6.5).
Examples of such other metal oxides include: praseodymium oxide,
dysprosium oxide, samarium oxide, cobalt oxide, zinc oxide,
neodymium oxide, yttrium oxide, ytterbium oxide, magnesium oxide,
nickel oxide, manganese oxide, lanthanum oxide, gadolinium oxide,
sodium oxide, dysprosium oxide, europium oxide, hafnium oxide, and
erbium oxide, as well as manganese oxide, chromium oxide, titanium
oxide, and ferric oxide which may or may not function as nucleating
agents.
Metal oxide precursors include metal nitrate salts, metal acetate
salts, metal citrate salts, metal formate salts, and metal chloride
salts. Metal nitrate, acetate, citrate, formate, and chloride salts
can be made by techniques known in the art, or obtained from
commercial sources such as Alfa Chemicals of Ward Hill, Mass. and
Mallinckrodt Chemicals of Paris, Ky. Examples of nitrate salts
include magnesium nitrate (Mg(NO.sub.3).sub.2.6H.sub.2 O), cobalt
nitrate (Co(NO.sub.3).sub.2.6H.sub.2 O), nickel nitrate
Ni(NO.sub.3).sub.2.6H.sub.2 O), lithium nitrate (LiNO.sub.3),
manganese nitrate (Mn(NO.sub.3).sub.2.4H.sub.2 O), chromium nitrate
(Cr(NO.sub.3).sub.3.9H.sub.2 O), yttrium nitrate
(Y(NO.sub.3).sub.3.6H.sub.2 O), praseodymium nitrate
(Pr(NO.sub.3).sub.3.6H.sub.2 O), samarium nitrate
(Sm(NO.sub.3).sub.3.6H.sub.2 O), neodymium nitrate
(Nd(NO.sub.3).sub.3.6H.sub.2 O), lanthanum nitrate
(La(NO.sub.3).sub.3.6H.sub.2 O), gadolinium nitrate
(Gd(NO.sub.3).sub.3.5H.sub.2 O), dysprosium nitrate
(Dy(NO.sub.3).sub.3.5H.sub.2 O), europium nitrate
(Eu(NO.sub.3).sub.3.6H.sub.2 O), ferric nitrate
(Fe(NO.sub.3).sub.3.9H.sub.2 O), zinc nitrate
(Zn(NO.sub.3).sub.3.6H.sub.2 O), and erbium nitrate
(Er(NO.sub.3).sub.3.5H.sub.2 O). Examples of metal acetate salts
include magnesium acetate, cobalt acetate, nickel acetate, lithium
acetate, manganese acetate, chromium acetate, yttrium acetate,
praseodymium acetate, samarium acetate, ytterbium acetate,
neodymium acetate, lanthanum acetate, gadolinium acetate, and
dysprosium acetate. Examples of citrate salts include magnesium
citrate, cobalt citrate, lithium citrate, and manganese citrate.
Examples of formate salts include magnesium formate, cobalt
formate, lithium formate, manganese formate, and nickel
formate.
Typically, the use of a metal oxide modifier may decrease the
porosity of the sintered abrasive grain and thereby increase the
density. Additionally certain metal oxide precursors (e.g.,
nucleating materials which are, or transform into, nucleating
agents, or materials that otherwise behave as nucleating agents)
may reduce the temperature at which the transitional aluminas
transform into alpha alumina. Certain metal oxides may react with
the alumina to form a reaction product and/or form crystalline
phases with the alpha alumina which may be beneficial during use of
the abrasive grain in abrading applications. Thus the selection and
amount of metal oxide will depend in part upon the processing
conditions and the desired abrading properties of the abrasive
grain.
The oxides of cobalt, nickel, zinc, and magnesium, for example,
typically react with alumina to form a spinel, whereas zirconia and
hafnia typically do not react with the alumina. Alternatively, for
example, the reaction products of dysprosium oxide and gadolinium
oxide with aluminum oxide are generally garnet. The reaction
products of praseodymium oxide, ytterbium oxide, erbium oxide, and
samarium oxide with aluminum oxide generally have a perovskite
and/or garnet structure. Yttria can also react with the alumina to
form Y.sub.3 Al.sub.5 O.sub.12 having a garnet crystal structure.
Certain rare earth oxides and divalent metal cations react with
alumina to form a rare earth aluminate represented by the formula
LnMAl.sub.11 O.sub.19, wherein Ln is a trivalent metal ion such as
La.sup.3+, Nd.sup.3+, Ce.sup.3+, Pr.sup.3+, Sm.sup.3+, Gd.sup.3+,
Er.sup.3+, or Eu.sup.3+, and M is a divalent metal cation such as
Mg.sup.2+, Mn.sup.2+, Ni.sup.2+, Zn.sup.2+, or Co.sup.2+. Such
aluminates have a hexagonal crystal structure. For additional
details regarding the inclusion of metal oxide (and/or precursors
thereof) in a boehmite dispersion see, for example, in U.S. Pat.
No. 4,314,827 (Leitheiser et al.), U.S. Pat. No. 4,770,671 (Monroe
et al.), U.S. Pat. No. 4,881,951 (Wood et al.), U.S. Pat. No.
5,429,647 (Larmie), U.S. Pat. No. 5,498,269 (Larmie), and U.S. Pat.
No. 5,551,963 (Larmie), the disclosures of which are incorporated
herein by reference.
Alumina-based dispersions (e.g., boehmite-based dispersions)
utilized in the practice of the present invention typically
comprise greater than 15% by weight (generally from greater than
20% to about 80% by weight; typically greater than 30% to about 80%
by weight) solids (or alternatively boehmite), based on the total
weight of the dispersion. Certain preferred dispersions, however,
comprise 35% by weight or more, 45% by weight or more, 50% by
weight or more, 55% by weight or more, 60% by weight or more and
65% by weight or more by weight or more solids (or alternatively
boehmite), based on the total weight of the dispersion. Weight
percents of solids and boehmite above about 80 wt-% may also be
useful, but tend to be more difficult to process to make the
abrasive grain provided by the method according to the present
invention.
General procedures for making sintered alpha alumina-based abrasive
grain are disclosed for example, in U.S. Pat. No. 4,518,397
(Leitheiser et al.), U.S. Pat. No. 4,770,671 (Monroe), U.S. Pat.
No. 4,744,802 (Schwabel), U.S. Pat. No. 5,139,978 (Wood), U.S. Pat.
No. 5,219,006 (Wood), and U.S. Pat. No. 5,593,647 (Monroe), the
disclosures of which are incorporated herein by reference.
The (initial) mixture is typically prepared by adding the various
it. components and then mixing them together to provide a
homogenous mixture. For example, boehmite is typically added to
water that has been mixed with nitric acid. The other components
are added before, during, or after the boehmite is added. However,
if the nucleating material is an aqueous, acidic dispersion of iron
oxyhydroxide and the silica source is a basic colloidal silica sol,
it is preferable not to add the two together, but rather to add
each individually to acidified water prior to, preferably, after
other components, such as the boehmite, have been added to the
acidified water.
A high solids dispersion is typically, and preferably, prepared by
gradually adding a liquid component(s) to a component(s) that is
non-soluble in the liquid component(s), while the latter is mixing
or tumbling. For example, a liquid containing water, nitric acid,
and metal salt may be gradually added to boehmite, while the latter
is being mixed such that the liquid is more easily distributed
throughout the boehmite.
Suitable mixers include pail mixers, sigma blade mixers, ball mill
and high shear mixers. Other suitable mixers may be available from
Eirich Machines, Inc. of Gurnee, Ill.; Hosokawa-Bepex Corp. of
Minneapolis, Minn. (including a mixer available under the trade
designation "SCHUGI FLEX-O-MIX", Model FX-160); and Littleford-Day,
Inc. of Florence, Ky.
Boehmite-based dispersions may be heated to increase the
dispersibility of the alpha alumina monohydrate and/or to create a
homogeneous dispersion. The temperature may vary to convenience,
for example the temperature may range from about 20.degree. C. to
80.degree. C., usually between 25.degree. C. to 75.degree. C.
Alternatively, the dispersion may be heated under a pressure
ranging from 1.5 to 130 atmospheres of pressure.
Boehmite-based dispersions typically gel prior to, or during,
drying. The addition of most modifiers may result in the dispersion
gelling faster. Alternatively, ammonium acetate or other ionic
species may be added to induce gelation of the dispersion. The pH
of the dispersion and concentration of ions in the gel generally
determines how fast the dispersion gels. Typically, the pH of the
dispersion is within a range of about 1.5 to about 5.
The dispersion may be extruded. It may be preferable to extrude
(typically a dispersion where at least 50 percent by weight of the
alumina content is provided by particulate (e.g., boehmite),
including in this context a gelled dispersion, or even partially
deliquified dispersion. The extruded dispersion, referred to as
extrudate, can be extruded into elongated precursor material (e.g.,
rods (including cylindrical rods and elliptical rods)). After
firing, the rods may have an aspect ratio between 1.5 to 10,
preferably between 2 to 6. Alternatively the extrudate may be in
the form of a very thin sheet, see for example U.S. Pat. No.
4,848,041 (Kruschke) herein after incorporated in by reference.
Examples of suitable extruders include ram extruders, single screw,
twin screw, and segmented screw extruders. Suitable extruders are
available, for example, from Loomis Products of Levitown, Pa.,
Bonnot Co. of Uniontown, Ohio., and Hosokawa-Bepex of Minneapolis,
Minn., which offers, for example, an extruder under the trade
designation "EXTRUD-O-MIX" (Model EM-6).
Preferably, the dispersion is compacted, for example, prior to or
during extrusion (wherein the extrusion step may inherently involve
compaction of the dispersion). In compacting the dispersion, it is
understood that the dispersion is subjected to a pressure or force
such as experienced, for example, in a pellitizer or die press
(including mechanical, hydraulic and pneumatic or presses) or an
extruder (i.e., all or substantially all of the dispersion
experiences the specified pressure). In general, compacting the
dispersion reduces the amount of air or gases entrapped in the
dispersion, which in turn generally produces a less porous
microstructure, that is more desirable. Additionally the compaction
step results an easier means to continuously feed the extruder and
thus may save on labor producing the abrasive grain.
If the elongated precursor material is a rod, it preferably has a
diameter such that the sintered abrasive grain will have a diameter
of, for example, about 150-5000 micrometers, and preferably, an
aspect ratio (i.e., length to width ratio) of at least 2.5:1, at
least 4:1, or even at least 5:1. The rod may have any cross
sectional shape including a circle, an oval, a star shape, a tube
and the like. The rod abrasive grain may also be curved.
A preferred apparatus for compacting the dispersion (gelled or not)
is illustrated in FIGS. 4-6. Modified segmented screw extruder 40,
has feed port 41 and auger 42 centrally placed within barrel 44.
FIG. 5 is a view of the interior of extruder 40 looking through
feed port 41. Barrel 44 has grooves (not shown; generally known as
"lands") running parallel down its length. Pins 48 extend centrally
into barrel 44. Further, helical flight 46 extends the length of
auger 42. Flight 46 is not continuous down the length of auger 42
but is segmented so that flight 46 on auger 42 does not come into
contact with pins 48.
The dispersion (including in this context gelled dispersion) (not
shown) is fed in feed port 41. Packer screw 43 urges the dispersion
against auger 42 so that the dispersion is compacted by auger 42
and extruded through die 49. Die 49 can have a variety of apertures
or holes therein (including a single hole or multiple holes). The
die apertures can be any of a variety of cross sectional shapes,
including a circle or polygon shapes (e.g., a square, star,
diamond, trapezoid, or triangle). The die apertures can be any of a
variety of sizes, but typically range from about 0.5 mm (0.02 inch)
to 1.27 cm (0.5 inch), and more typically, from about 0.1 cm (0.04
inch) to about 0.8 cm (0.3 inch).
The extruded dispersion can be can be cut or sliced, for example,
to provide discrete particles, and/or to provide particles having a
more uniform length. Examples of methods for cutting (or slicing)
the dispersion include rotary knife, blade cutters and wire
cutters. The compacted dispersion can also be shredded and/or
grated.
In general, techniques for drying the dispersion are known in the
art, including heating to promote evaporation of the liquid medium,
or simply drying in air. The drying step generally removes a
significant portion of the liquid medium from the dispersion;
however, there still may be a minor portion (e.g., about 10% or
less by weight) of the liquid medium present in the dried
dispersion. Typical drying conditions include temperatures ranging
from about room temperature to over about 200.degree. C., typically
between 50 to 150.degree. C. The times may range from about 30
minutes to over days. To minimize salt migration, it may be
desirable to dry the dispersion at low temperature.
After drying, the dried mixture (e.g., dispersion) may be converted
into precursor particles. One typical means to generate these
precursor particles is by a crushing technique. Various crushing or
comminuting techniques may be employed such as a roll crusher, jaw
crusher, hammer mill, ball mill and the like. Coarser particles may
be recrushed to generate finer particles. It is also preferred that
the dried dispersion be crushed, as, for example, it is generally
easier to crush dried gel versus the sintered alpha alumina based
abrasive grain.
Alternatively, for example, the mixture may be converted into
precursor particles prior to drying. This may occur for instance if
the mixture is processed into a desired grit shape and particle
size distribution. For example, the dispersion may be extruded into
rods that are subsequently cut to the desired lengths and then
dried. Alternatively, the mixture may be molded into a triangular
shape particle and then dried. Additional details concerning
triangular shaped particles may be found in U.S. Pat. No. 5,201,916
(Berg et al.), the disclosure of which is incorporated herein by
reference.
Alternatively, for example, the dried mixture (e.g., dispersion) is
shaped into lumps with a high volatilizable content which then are
explosively communited by feeding the lumps directly into a furnace
held at a temperature above 350.degree. C., usually a temperature
between 600.degree. C. to 900.degree. C.
Typically, the dried mixture is calcined, prior to sintering,
although a calcining step is not always required. In general,
techniques for calcining the dried mixture or ceramic precursor
material, wherein essentially all the volatiles are removed, and
the various components that were present in the dispersion are
transformed into oxides, are known in the art. Such techniques
include using a rotary or static furnace to heat dried mixture at
temperatures ranging from about 400-1000.degree. C. (typically from
about 450-800.degree. C.) until the free water, and typically until
at least about 90 wt-% of any bound volatiles are removed.
It is also within the scope of the present invention, and a part of
at least one method according to the present invention, to
impregnate a metal oxide modifier source (typically a metal oxide
precursor) into a calcined precursor particle. For example, in at
least one method according to the present invention, zirconia
precursor (e.g., a zirconium salt) can be impregnated into
precursor material. Typically, the metal oxide precursors are in
the form metal salts. These metal oxide precursors and metal salts
are described above with respect to the initial mixture.
Methods of impregnating sol gel-derived particles are described in
general, for example, in U.S. Pat. No. 5,164,348 (Wood), the
disclosure of which is incorporated herein by reference. In
general, ceramic precursor material (i.e., dried alumina-based
mixture (or dried ceramic precursor material), or calcined
alumina-based mixture (or calcined ceramic precursor material)) is
porous. For example, a calcined ceramic precursor material
typically has pores about 2-15 nanometers in diameter extending
therein from an outer surface. The presence of such pores allows an
impregnation composition comprising a mixture comprising liquid
medium (typically water) and appropriate metal precursor to enter
into ceramic precursor material. The metal salt material is
dissolved in a liquid, and the resulting solution mixed with the
porous ceramic precursor particle material. The impregnation
process is thought to occur through capillary action.
The liquid used for the impregnating composition is preferably
water (including deionized water), an organic solvent, and mixtures
thereof. If impregnation of a metal salt is desired, the
concentration of the metal salt in the liquid medium is typically
in the range from about 5% to about 40% dissolved solids, on a
theoretical metal oxide basis). Preferably, there is at least 50 ml
of solution added to achieve impregnation of 100 grams of porous
precursor particulate material, more preferably, at least about 60
ml of solution to 100 grams of precursor particulate material.
After the impregnation, the resulting impregnated precursor
particle is typically calcined to remove any volatiles prior to
sintering. The conditions for this calcining step are described
above.
After the precursor particle is formed or optionally calcined, the
precursor particle is sintered to provide a dense, ceramic alpha
alumina based abrasive grain. In general, techniques for sintering
the precursor material, which include heating at a temperature
effective to transform transitional alumina(s) into alpha alumina,
to causing all of the metal oxide precursors to either react with
the alumina or form metal oxide, and increasing the density of the
ceramic material, are known in the art. The precursor material may
be sintered by heating (e.g., using electrical resistance,
microwave, plasma, laser, or gas combustion, on batch basis or a
continuous basis. Sintering temperatures are usually range from
about 1200.degree. C. to about 1650.degree. C.; typically, from
about 1200.degree. C. to about 1500.degree. C.; more typically,
less than 1400.degree. C. The length of time which the precursor
material is exposed to the sintering temperature depends, for
example, on particle size, composition of the particles, and
sintering temperature. Typically, sintering times range from a few
seconds to about 60 minutes (preferably, within about 3-30
minutes). Sintering is typically accomplished in an oxidizing
atmosphere, although inert or reducing atmospheres may also be
useful.
The longest dimension of the alpha alumina-based abrasive grain is
typically at least about 1 micrometer. The abrasive grain described
herein can be readily made with a length of greater than about 50
micrometers, and larger abrasive grain (e.g., greater than about
1000 micrometers or even greater than about 5000 micrometers) can
also be readily made. Generally, the preferred abrasive grain has a
length in the range from about 100 to about 5000 micrometers
(typically in the range from about 100 to about 3000 micrometers),
although other sizes are also useful, and may even be preferred for
certain applications. In another aspect, abrasive grain according
to the present invention, typically have an aspect ratio of at
least 1.2:1 or even 1.5:1, sometimes at least 2:1, and
alternatively, at least 2.5:1.
Dried, calcined, and/or sintered materials provided during or by
the method according to the present invention, are typically
screened and graded using techniques known in the art. For example,
the dried particles are typically screened to a desired size prior
to calcining. Sintered abrasive grain are typically screened and
graded prior to use in an abrasive application or incorporation
into an abrasive article.
Screening and grading of abrasive grain made according to the
method of the present invention can be done, for example, using the
well known techniques and standards for ANSI (American National
Standard Institute), FEPA (Federation Europeenne des Fabricants de
Products Abrasifs), or JIS (Japanese Industrial Standard) grade
abrasive grain.
It is also within the scope of the present invention to recycle
unused (typically particles too small in size to provide the
desired size of sintered abrasive grain) deliquified mixture
(typically dispersion) material as generally described, for
example, in U.S. Pat. No. 4,314,827 (Leitheiser et al.), the
disclosure of which is incorporated herein by reference. For
example, a first dispersion can be made as described above, dried,
crushed, and screened, and then a second dispersion made by
combining, for example, liquid medium (preferably, aqueous),
boehmite, and deliquified material from the first dispersion, and
optionally metal oxide and/or metal oxide precursor. The recycled
material may provide, on a theoretical metal oxide basis, for
example, at least 10 percent, at least 30 percent, at least 50
percent, or even up to (and including) 100 percent of the
theoretical Al.sub.2 O.sub.3 content of the dispersion which is
deliquified and converted (including calcining and sintering) to
provide the sintered abrasive grain.
In one aspect of the invention, the abrasive grain may be processed
such that it is "sharp". The term sharp is known to one skilled in
the abrasive grain art. In general, a sharp abrasive grain is
elongated in shape, preferably needle-like. Another way to describe
a sharp abrasive grain is a grain that is in the form of sliver or
shard. A sharp abrasive grain does not have a blocky shape
associated with it. It is preferred that the sharp abrasive grain
have "pointy" ends (i.e., the faces forming the ends of the
abrasive grain meet at a point). Additionally, it is preferred that
the sharp abrasive grain has angular faces. In some abrading
applications, relatively sharp abrasive grain may be preferred.
There are several techniques to measure the sharpness of an
abrasive grain, including bulk density and aspect ratio. The bulk
density of the abrasive grain can be measured, for example, in
accordance with ANSI Standard B74.4-1992, published November, 1992,
the disclosure of which is incorporated herein by reference.
The aspect ratio, which is also an indication of sharpness, is
determined as the length of an abrasive grain divided by the cross
sectional width. Typically, sharp abrasive grain have an aspect
ratio of at least one to one, preferably at least about 1.5 to 1
and preferably about 2 to 1. In some instances, the aspect ratio
may be greater than 3 to 1.
It is also within the scope of the present invention to coat the
abrasive grain with a surface coating such as described in U.S.
Pat. No. 1,910,440 (Nicholson), U.S. Pat. No. 3,041,156 (Rowse),
U.S. Pat. No. 5,009,675 (Kunz et al.), U.S. Pat. No. 4,997,461
(Markhoff-Matheny et al.), and U.S. Pat. No. 5,042,991 (Kunz et
al.), U.S. Pat. No. 5,011,508 (Wald et al.), and U.S. Pat. No.
5,213,591 (Celikkaya et al.), the disclosures of which are
incorporated herein by reference.
Abrasive grain according to the present invention can be used in
conventional abrasive products, such as coated abrasive products,
bonded abrasive products (including vitrified and resinoid grinding
wheels, cutoff wheels, and honing stones), nonwoven abrasive
products, and abrasive brushes. Typically, abrasive products (i.e.,
abrasive articles) include binder and abrasive grain, at least a
portion of which is abrasive grain according to the present
invention, secured within the abrasive product by the binder.
Methods of making such abrasive products and using abrasive
products are well known to those skilled in the art. Furthermore,
abrasive grain according to the present invention can be used in
abrasive applications that utilize slurries of abrading compounds
(e.g., polishing compounds).
Coated abrasive product generally include a backing, abrasive
grain, and at least one binder to hold the abrasive grain onto the
backing. The backing can be any suitable material, including cloth,
polymeric film, fibre, nonwoven webs, paper, combinations thereof,
and treated versions thereof. The binder can be any suitable
binder, including an inorganic or organic binder. The abrasive
grain can be present in one layer or in two layers of the coated
abrasive product. Methods of making coated abrasive products are
described, for example, in U.S. Pat. No. 4,734,104 (Broberg), U.S.
Pat. No. 4,737,163 (Larkey), U.S. Pat. No. 5,203,884 (Buchanan et
al.), U.S. Pat. No. 5,378,251 (Culler et al.), U.S. Pat. No.
5,417,726 (Stout et al.), U.S. Pat. No. 5,436,063 (Follett et al.),
U.S. Pat. No. 5,496,386 (Broberg et al.), and U.S. Pat. No.
5,520,711 (Helmin), the disclosures of which are incorporated
herein by reference.
An example of a coated abrasive product is depicted in FIG. 1.
Referring to this figure, coated abrasive product 1 has a backing
(substrate) 2 and abrasive layer 3. Abrasive layer 3 includes
abrasive grain 4 secured to a major surface of backing 2 by make
coat 5 and size coat 6. In some instances, a supersize coat (not
shown) is used.
Bonded abrasive products typically include a shaped mass of
abrasive grain held together by an organic, metallic, or vitrified
binder. Such shaped mass can be, for example, in the form of a
wheel, such as a grinding wheel or cutoff wheel. It can also be in
the form, for example, of a honing stone or other conventional
bonded abrasive shape. It is typically in the form of a grinding
wheel. Referring to FIG. 2, grinding wheel 10 is depicted, which
includes abrasive grain 11, at least a portion of which is abrasive
grain according to the present invention, molded in a wheel and
mounted on hub 12. For further details regarding bonded abrasive
products, see, for example, U.S. Pat. No. 4,997,461
(Markhoff-Matheny et al.) and U.S. Pat. No. 4,898,597 (Hay et al.),
the disclosures of which are incorporated herein by reference.
Nonwoven abrasive products typically include an open porous lofty
polymer filament structure having abrasive grain distributed
throughout the structure and adherently bonded therein by an
organic binder. Examples of filaments include polyester fibers,
polyamide fibers, and polyaramid fibers. In FIG. 3, a schematic
depiction, enlarged about 100x, of a typical nonwoven abrasive
product is provided. Such a nonwoven abrasive product comprises
fibrous mat 50 as a substrate, onto which abrasive grain 52, at
least a portion of which is abrasive grain according to the present
invention, are adhered by binder 54. For further details regarding
nonwoven abrasive products, see, for example, U.S. Pat. No.
2,958,593 (Hoover et al.), the disclosure of which is incorporated
herein by reference.
Useful abrasive brushes include those having a plurality of
bristles unitary with a backing (see, e.g., U.S. Pat. No. 5,679,067
(Johnson et al.), the disclosure of which is incorporated herein by
reference). Preferably, such brushes are made by injection molding
a mixture of polymer and abrasive grain.
Suitable organic binders for the abrasive products include
thermosetting organic polymers. Examples of suitable thermosetting
organic polymers include phenolic resins, urea-formaldehyde resins,
melamine-formaldehyde resins, urethane resins, acrylate resins,
polyester resins, aminoplast resins having pendant
.alpha.,.beta.-unsaturated carbonyl groups, epoxy resins, and
combinations thereof. The binder and/or abrasive product can also
include additives such as fibers, lubricants, wetting agents,
thixotropic materials, surfactants, pigments, dyes, antistatic
agents (e.g., carbon black, vanadium oxide, graphite, etc.),
coupling agents (e.g., silanes, titanates, zircoaluminates, etc.),
plasticizers, suspending agents, and the like. The amounts of these
optional additives are selected to provide the desired properties.
The coupling agents can improve adhesion to the abrasive grain
and/or filler.
The binder can also contain filler materials or grinding aids,
typically in the form of a particulate material. Typically, the
particulate materials are inorganic materials. Examples of
particulate materials that act as fillers include metal carbonates,
silica, silicates, metal sulfates, metal oxides, and the like.
Examples of particulate materials that act as grinding aids
include: halide salts such as sodium chloride, potassium chloride,
sodium cryolite, and potassium tetrafluoroborate; metals such as
tin, lead, bismuth, cobalt, antimony, iron, and titanium; organic
halides such as polyvinyl chloride and tetrachloronaphthalene;
sulfur and sulfur compounds; graphite; and the like. A grinding aid
is a material that has a significant effect on the chemical and
physical processes of abrading, which results in improved
performance. In a coated abrasive product, a grinding aid is
typically used in the supersize coat applied over the surface of
the abrasive grain, although it can also be added to the size coat.
Typically, if desired, a grinding aid is used in an amount of about
50-300 g/m.sup.2 (preferably, about 80-160 g/m.sup.2) of coated
abrasive product.
The abrasive products can contain 100% abrasive grain according to
the present invention, or they can contain a blend of such abrasive
grain with conventional abrasive grain and/or diluent particles.
However, at least about 5% by weight, and preferably about 30-100%
by weight, of the abrasive grain in the abrasive products should be
abrasive grain according to the present invention. Examples of
suitable conventional abrasive grain include fused aluminum oxide,
silicon carbide, diamond, cubic boron nitride, garnet, fused
alumina zirconia, and other sol-gel abrasive grain, and the like.
Examples of suitable diluent particles include marble, gypsum,
flint, silica, iron oxide, aluminum silicate, glass, and diluent
agglomerates. Abrasive grain according to the present invention can
also be combined in or with abrasive agglomerates. An example of an
abrasive agglomerate is described in U.S. Pat. No. 4,311,489
(Kressner), U.S. Pat. No. 4,652,275 (Bloecher et al.), and U.S.
Pat. No. 4,799,939 (Bloecher et al.), the disclosures of which are
incorporated herein by reference.
EXAMPLES
This invention is further illustrated by the following examples,
but the particular materials and amounts thereof recited in these
examples, as well as other conditions and details, should not be
construed to unduly limit this invention. Various modifications and
alterations of the invention will become apparent to those skilled
in the art. All parts and percentages are by weight unless
otherwise indicated.
Any reference to the percent solids levels of the dispersion used
in the following examples are the approximate solids levels, as
they do not take into account the 2-6% water commonly found on the
surface of boehmite, nor the solids provided by any non-boehmite
additives.
The following designations are used in the examples:
AAMH alpha-alumina monohydrate (boehmite) (obtained from Condea
Chemie, Hamburg, Germany, under the trade designation "DISPERAL");
dispersability value: 99.0% DWT deionized water that was at a
temperature of 60-65.degree. C., unless otherwise specified
HNO.sub.3 nitric acid, 70% concentrated IO iron oxyhydroxide
(alpha-FeOOH), aqueous dispersion (pH = 5.0-5.5) about 90-95% of
which is goethite, acicular particles with an average particle size
of about 0.05 to 0.1 micrometer, a length to diameter or width
ratio of about 1:1 to 3:1, and a surface area of about 100 m.sup.2
/g; dispersion yields 3% to 7% by weight Fe.sub.2 O.sub.3 H-30
alpha-alumina monohydrate (boehmite) (obtained from Alcoa
Industrial Chemicals, Houston, TX, under the trade designation
"HIQ-30") CS1 basic colloidal silica, 15% solids, (obtained from
Eka Nobel, Inc. of Augusta, GA, under the trade designation "NYACOL
215"); average particle size 5 nm CS2 colloidal silica, 30% by
weight solids (obtained from Nyacol Products, Inc. of Ashland, MA
under the trade designation "NYACOL 830"); average particle size
8-10 nm MGN solution of magnesium nitrate (from Mallinckrodt
Chemical, Paris, KY) in water containing, on a theoretical metal
oxides basis, 10.5% MgO ZRO zirconia sol containing 20% solid by
weight ZrO.sub.2 (obtained from Nyacol Products, Inc. of Ashland,
MA under the trade designation "ZR100/20"); average particle size
100 nm ZRO2 zirconia sol containing 20% solid by weight (obtained,
from Nyacol Products, Inc. under the trade designation "ZR10/20");
average particle size 5-10 nm ZRN zirconyl acetate solution (on a
theoretical metal oxides basis, .about.22% ZrO.sub.2 ; obtained
from Magnesium Electron, Inc. of Flemington, NJ)
Example 1
A dispersion was made by mixing together 600 grams of AAMH, 375
grams of ZRO, 46 grams of CS1, 36 grams of HN.sub.3, 100 grams of
IO having 6.5% iron oxide (calculated on a theoretical metal oxide
basis as Fe.sub.2 O.sub.3), and 1,650 grams of DWT in a
conventional 4 liter, food grade blender (Waring blender available
from Waring Products Division, Dynamics Corp. of America, New
Hartford, Conn.; Model 34BL22(CB6)). The DWT, HNO.sub.3, ZRO, CS1,
and IO were placed in the blender and mixed. The AAMH was then
added, and the contents mixed at low speed setting for 60
seconds.
The resulting dispersion was transferred into glass trays (obtained
under the trade designation "PYREX") and allowed to gel at room
temperature. The gelled dispersion was then dried overnight at
approximately 93.degree. C. (200.degree. F.) to provide dried,
friable solid, material. The dried material was crushed using
pulverizer (having a 1.1 mm gap between the steel plates; obtained
under the trade designation "BRAUN" Type UD from Braun Corp., Los
Angeles, Calif.) to provide precursor abrasive grain (particles).
The crushed material was screened to retain the particles that were
between about 0.25 to 1 mm in size.
The retained particles were fed into a rotary calcining kiln to
provide calcined abrasive grain precursor material. The calcining
kiln consisted of a 15 cm inner diameter, 1.2 meter in length,
stainless steel tube having a 0.3 meter hot zone. The tube was
inclined at a 3.0 degree angle with respect to the horizontal. The
tube rotated at about 3.5 rpm, to provide a residence time in the
tube of about 4-5 minutes. The temperature of the hot zone was
about 650.degree. C.
The calcined abrasive grain precursor was fed into a rotary
sintering kiln. The sintering kiln consisted of an 8.9 cm inner
diameter, 1.32 meter long silicon carbide tube inclined at 4.4
degrees with respect to the horizontal and had a 31 cm hot zone.
The heat was applied externally via SiC electric heating elements.
The sintering kiln rotated at 5.0 rpm, to provide a residence time
in the tube of about 7 minutes. The sintering temperature was about
1400.degree. C. The product exited the kiln into room temperature
air where it was collected in a metal container and allowed to cool
to room temperature. The composition of the sintered abrasive
grain, based on the formulation used to make the grain, was, on a
theoretical metal oxide basis, 83% by weight Al.sub.2 O.sub.3, 14%
by weight ZrO.sub.2, 1.5% by weight SiO.sub.2, and 1.5% by weight
Fe.sub.2 O.sub.3, based on the total metal oxide content of the
sintered abrasive grain.
A fracture surface of an Example 1 abrasive grain was examined
using a scanning electron microscope (SEM). The average size of the
alpha alumina crystallites was observed to be less than one
micrometer. Further, an Example 1 abrasive grain was mounted and
polished with a conventional polisher (obtained from Buehler of
Lake Bluff, Ill. under the trade designation "ECOMET 3 TYPE
POLISHER-GRINDER"). The sample was polished for about 3 minutes
with a diamond wheel, followed by three minutes of polishing with
each of 45, 30, 15, 9, 3, and 1 micrometer diamond slurries. The
polished sample was examined using SEM in the backscattered mode.
The average size of the zirconia crystallites was observed to be
less than 0.25 micrometer. In addition, the SEM analysis indicated
that the microstructure was dense and uniform.
The sintered alpha alumina-based ceramic abrasive grain was graded
to retain the -35+40 mesh fraction (U.S.A. Standard Testing
Sieves). This retained abrasive grain was incorporated into coated
abrasive discs, which were tested for grinding performance. The
coated abrasive discs were made according to conventional
procedures. The abrasive grain were bonded to 17.8 cm diameter, 0.8
mm thick vulcanized fiber backings (having a 2.2 cm diameter center
hole) using a conventional calcium carbonate-filled phenolic make
resin (48% resole phenolic resin, 52% calcium carbonate, diluted to
81% solids with water) and a conventional cryolite-filled phenolic
size resin (32% resole phenolic resin, 2% iron oxide, 66% cryolite,
diluted to 78% solids with water). The wet make resin weight was
about 185 g/m.sup.2. Immediately after the make coat was applied,
the abrasive grain were electrostatically coated. The make resin
was precured for 90 minutes at 88.degree. C. The wet size weight
was about 850 g/m.sup.2. The size resin was precured for 90 minutes
at 88.degree. C., followed by a final cure of 10 hours at
100.degree. C. The fibre discs were flexed prior to testing.
Comparative Example A
Comparative Example A coated abrasive discs were prepared as
described for Example 1 except the dispersion, which did not
include ZRO, consisted of 600 grams of AAMH, 46 grams of CS1, 36
grams of HNO.sub.3, 100 grams of IO having 6.5% iron oxide
(calculated on a theoretical metal oxide basis as Fe.sub.2
O.sub.3), and 1,450 grams of DWT, the sintering temperature was
1440.degree., and the sintering kiln rotated at 2 rpm, to provide a
residence time in the tube of about 15 minutes. The composition of
the sintered abrasive grain, based on the formulation used to make
the grain, was, on a theoretical metal oxide basis, 97% by weight
Al.sub.2 O.sub.3, 1.5% by weight SiO.sub.2, and 1.5% by weight
Fe.sub.2 O.sub.3, based on the total metal oxide content of the
sintered abrasive grain.
Comparative Example B
Comparative Example B coated abrasive discs were prepared as
described for Comparative Example A except (a) the dispersion did
not include CS1, and (b) the crushed calcined precursor particles
were impregnated with MGN (47 grams of MGN diluted to 60 ml with
DWT for each 100 grams of calcined precursor), calcined a second
time, and was sintered at 1350.degree., wherein the sintering kiln
rotated at 2 rpm to provide a residence time in the tube of about
15 minutes. The composition of the sintered abrasive grain, based
on the formulation used to make the grain, was, on a theoretical
metal oxide basis, 94% by weight Al.sub.2 O.sub.3, 4.5 by weight
MgO, and 1.5% by weight Fe.sub.2 O.sub.3, based on the total metal
oxide content of the sintered abrasive grain.
Example 2
A solution was made by mixing together 625 grams of ZRO, 75 grams
of CS1, 60 grams of HNO.sub.3, 175 grams of IO having 6.5% iron
oxide (calculated on a theoretical metal oxide basis as Fe.sub.2
O.sub.3). 1000 grams of AAMH were fed into a 19 liter (5 gallon)
pail rotating at 55 rpm and inclined 28.degree. longitudinally
continuously and simultaneously as a stream of the solution was
sprayed onto the AAMH. Agglomerated balls about 3-5 mm in diameter
were formed at about 60% solid. The agglomerated balls were fed
into a catalyst extruder (available from Bonnot Co. of Uniontown,
Ohio) and extruded through a die having thirty six 0.254 cm (0.1
inch) diameter openings. The pressure inside the extruder, measured
directly next to the die, was about 410-477 kg/cm.sup.2 (1200-1400
psi). The extruded material was placed on a conveyer belt which fed
into a drying oven that was at about 93.degree. C. (200.degree.
F.). The resulting dried, friable, solid material was crushed,
screened, calcined, and sintered as described for Example 1. The
composition of the sintered abrasive grain, based on the
formulation used to make the abrasive grain, was, on a theoretical
metal oxide basis, 83% by weight Al.sub.2 O.sub.3, 14% by weight
ZrO.sub.2, 1.5 by weight SiO.sub.2, and 1.5% by weight Fe.sub.2
O.sub.3, based on the total metal oxide content of the sintered
abrasive grain.
Example 2 abrasive grain were examined using the SEM as described
in Example 1. The average size of the alpha alumina crystallites
was observed to be less than 1 micrometer; the average size of the
zirconia crystallites less than 0.25 micrometer. In addition, the
SEM analysis indicated that the microstructure was dense and
uniform.
The sintered alpha alumina-based ceramic abrasive grain was graded
to retain the -30+35 and -35+40 mesh fractions (U.S.A. Standard
Testing Sieves). These fractions were blended in a 1:1 ratio and
incorporated into coated abrasive discs, which were tested for
grinding performance. The coated abrasive discs were made as
described in Example 1.
Comparative Example C
Comparative Example C was prepared as described for Example 2
except the dispersion, which did not include ZRO, consisted of
1,000 grams of AAMH, 75 grams of CS1, 60 grams of HNO.sub.3, 175
grams of IO having 6.5% iron oxide (calculated on a theoretical
metal oxide basis as Fe.sub.2 O.sub.3), and 400 grams of DWT; and
it was sintered as described for Comparative Example A. The
composition of the sintered abrasive grain, based on the
formulation used to make the grain, was, on a theoretical metal
oxide basis, 97% by weight Al.sub.2 O.sub.3, 1.5 by weight
SiO.sub.2, and 1.5% by weight Fe.sub.2 O.sub.3, based on the total
metal oxide content of the sintered abrasive grain.
Example 3
Example 3 was prepared as described for Example 1 except the
dispersion consisted of 600 grams of AAMH, 95 grams of ZRO2, 46
grams of CS 1, 36 grams of HNO.sub.3, 100 grams of IO having 6.5%
iron oxide (calculated on a theoretical metal oxide basis as
Fe.sub.2 O.sub.3), and 1,650 grams of DWT; and the sintering kiln
rotated at 2 rpm. The composition of the sintered abrasive grain,
based on the formulation used to make the grain, was, on a
theoretical metal oxide basis, 93% by weight Al.sub.2 O.sub.3, 4%
by weight ZrO.sub.2, 1.5 by weight SiO.sub.2, and 1.5% by weight
Fe.sub.2 O.sub.3, based on the total metal oxide content of the
sintered abrasive grain.
Example 3 abrasive grain were examined using the SEM as described
in Example 1. The average size of the alpha alumina crystallites
was observed to be less than 1 micrometer; the average size of the
zirconia crystallites less than 0.25 micrometer. In addition, the
SEM analysis indicated that the microstructure was dense and
uniform.
Example 4
Example 4 was prepared as described for Example I except the
dispersion consisted of 600 grams of AAMH, 185 grams of ZRO2, 46
grams of CS1, 36 grams of HNO.sub.3, 100 grams of IO having 6.5%
iron oxide (calculated on a theoretical metal oxide basis as
Fe.sub.2 O.sub.3), and 1,650 grams of DWT; and the sintering kiln
rotated at 2 rpm. The composition of the sintered abrasive grain,
based on the formulation used to make the grain, was, on a
theoretical metal oxide basis, 89.5% by weight Al.sub.2 O.sub.3,
7.5% by weight ZrO.sub.2, 1.5 by weight SiO.sub.2, and 1.5% by
weight Fe.sub.2 O.sub.3, based on the total metal oxide content of
the sintered abrasive grain.
Example 4 abrasive grain were examined using the SEM as described
in Example 1. The average size of the alpha alumina crystallites
was observed to be less than 1 micrometer; the average size of the
zirconia crystallites less than 0.25 micrometer. In addition, the
SEM analysis indicated that the microstructure was dense and
uniform.
Grinding Performance Evaluation of Examples 1-4 and Comparative
Examples A-C
The grinding performance of Example 1 and Comparative Example A and
B coated abrasive discs were evaluated according to the following
test procedure. Each coated abrasive disc was mounted on a beveled
aluminum back-up pad, and used to grind the face of a pre-weighed
1.25 cm.times.18 cm.times.10 cm 1018 mild steel workpiece. The disc
was driven at 5,000 rpm while the portion of the disc overlaying
the beveled edge of the back-up pad contacted the workpiece at a
load of 10.88 kg (24 lbs.). Each disc was used to grind individual
workpiece in sequence for one-minute intervals. The total cut was
the sum of the amount of material removed from the workpieces
throughout the test period. Two discs were tested for each example.
The results, which are averages of the discs tested, are summarized
in Table 1, below.
TABLE 1 Metal Removed For The Example Total Cut, g 12th minute, g
Comparative Example A* 1524 67 Comparative Example B 1622 88 1 2066
113 *testing of Comparative Example A was discontinued after 10
minutes due to the relatively low cut rate; the cut for the
10.sup.th minute was 67 grams
The grinding performance of Example 2 and Comparative Example C
coated abrasive discs were evaluated as described for Example 1
(above). Two discs were tested for each example. The results, which
are averages of the discs tested, are summarized in Table 2,
below.
TABLE 2 Example Total Cut, g Comparative Example C 1047 Example 2
1324
The grinding performance of Example 3 and 4, and Comparative
Example C, coated abrasive discs were evaluated as described for
Example 1 (above), except the load during grinding was 7.73 Kg (17
lbs.). Two discs were tested for each example. The results, which
are averages of the discs tested, are summarized in Table 3,
below.
TABLE 3 Example Total Cut, g Comparative Example A 1669 3 1721 4
2030
Example 5
Example 5 sintered abrasive was prepared as described for Example 2
except the solution consisted of 2,650 grams of ZRN, 750 grams of
CS2, 1,250 grams of HNO.sub.3, 5,000 grams of IO having 4.7% iron
oxide (calculated on a theoretical metal oxide basis as Fe.sub.2
O.sub.3), and 2,400 grams of DWT, and 18,000 grams of H-30 were
used in place of the AAMH; and the sintering kiln rotated at 2 rpm.
The composition of the sintered abrasive grain, based on the
formulation used to make the grain, was, on a theoretical metal
oxide basis, 93% Al.sub.2 O.sub.3, 4% ZrO.sub.2, 1.5 SiO.sub.2, and
1.5% Fe.sub.2 O.sub.3, based on the total metal oxide content of
the sintered abrasive grain.
Example 5 abrasive grain were examined using the SEM as described
in Example 1. The average size of the alpha alumina crystallites
was observed to be less than 1 micrometer; the average size of the
zirconia crystallites less than 0.25 micrometer. In addition, the
SEM analysis indicated that the microstructure was dense and
uniform.
The alpha alumina ceramic abrasive grain, which was graded into a
1:1 mix of -30+35 and -35+40 mesh fractions (U.S.A. Standard
Testing Sieves), was incorporated into 439 cm.times.335 cm
(173".times.132") resin-treated YF weight cloth belts. The make and
size resins, which were the same as those for Example 1, were
precured and cured as described in Example 1. The wet make and size
weights were about 185 g/m.sup.2 and about 850 g/m.sup.2,
respectively. The cured belt material was then converted into 2.5
cm.times.100 cm (1".times.40") belts. The coated abrasive belts
were flexed prior to testing.
Example 6
Example 6 was prepared as described for Example 5 except the
dispersion consisted of 18,000 grams of H-30, 4,750 grams of ZRN,
750 grams of CS2, 1,250 grams of HNO.sub.3, 5,000 grams of IO
having 4.7% iron oxide (calculated on a theoretical metal oxide
basis as Fe.sub.2 O.sub.3), and 1,250 grams of DWT. The composition
of the sintered abrasive grain, based on the formulation used to
make the grain, was, on a theoretical metal oxide basis, 90% by
weight Al.sub.2 O.sub.3, 7% by weight ZrO.sub.2, 1.5% by weight
SiO.sub.2, and 1.5% by weight Fe.sub.2 O.sub.3, based on the total
metal oxide content of the abrasive grain.
Example 6 abrasive grain were examined using the SEM as described
in Example 1. FIG. 7 is a photomicrograph of a fracture surface of
the Example 6 abrasive grain showing the alpha alumina crystallites
61. FIG. 8 is a photomicrograph a polished section of Example 6
abrasive grain in the back scattered mode showing zirconia
crystallites 63. The average size of the alpha alumina crystallites
was observed to be less than 1 micrometer; the average size of the
zirconia crystallites less than 0.25 micrometer. In addition, the
SEM analysis indicated that the microstructure was dense and
uniform.
Example 7
Example 7 was prepared as described for Example 5 except the
dispersion consisted of 18,000 grams of H-30, 7,000 grams of ZRN,
750 grams of CS2, 1,250 grams of HNO.sub.3, 5,000 grams of IO
having 4.7% iron oxide (calculated on a theoretical metal oxide
basis as Fe.sub.2 O.sub.3). The composition of the sintered
abrasive grain, based on the formulation used to make the grain,
was on a theoretical oxide basis, 87% by weight Al.sub.2 O.sub.3,
10% by weight ZrO.sub.2, 1.5% by weight SiO.sub.2, and 1.5% by
weight Fe.sub.2 O.sub.3, based on the total metal oxide content of
the abrasive grain.
Example 7 abrasive grain were examined using the SEM as described
in Example 1. The average size of the alpha alumina crystallites
was observed to be less than 1 micrometer; the average size of the
zirconia crystallites less than 0.25 micrometer. In addition, the
SEM analysis indicated that the microstructure was dense and
uniform.
Comparative Example D
The Comparative Example D belt was prepared as described for
Example 5, except the abrasive used was a sol-gel-derived alpha
alumina ceramic abrasive grain available from the 3M Company under
the trade designation "201 CUBITRON". This type of abrasive grain
is designed to be used in high pressure grinding applications.
Grinding Performance Evaluation of Examples 5-7 and Comparative
Example D
The grinding performance of Example 5-7 and Comparative Example D
coated abrasive belts were evaluated according to the following
test procedure. The 2.5cm.times.100 cm (1".times.40") belts were
placed around a metal wheel of a belt grinder (obtained under the
trade designation "SPA2030ND" from Elb Grinders Corporation of
Mountainside, N.J.). The metal wheel was rotating at a speed of
1,700 smm (surface meters per minute). The 1018 mild steel
workpieces (1.3 cm.times.10.2 cm.times.35.6 cm
(0.5".times.4".times.14") dimension) were mounted on a bed
oscillating at a speed of 6 mpm (meters per minute). The belt was
tested at a predetermined infeed rate for each pass. The workpieces
were water cooled after each pass. The normal grinding forces were
monitored. When the normal grinding force reached 23 kgf, the
grinding test was ended. The amount of metal removed for each belt
was determined. Two belts were tested for each example, except that
four belts were tested for Example 6. The results, which are
averages of the belts tested, are summarized in Table 4, below.
TABLE 4 Metal Removed at 152.4 Metal Removed at 177.8 micrometer (6
mils) infeed micrometer (7 mils) infeed Example rate, g rate, g
Comparative D 1022 1113 5 2433 1427 6 2633 1723 7 2336 1532
For the particular test, the 152.4 micrometer (6 mils) infeed
represents a relatively low grinding pressure application, and the
177.8 micrometer (7 mils) infeed a relatively high grinding
pressure application.
Examples 8 and 9 and Comparative Example E
Examples 8 and 9 abrasive grain were prepared as described for
Examples 5 and 6, except the sintered alpha alumina-based abrasive
grain used to make the coated abrasive belts were graded into a 1:1
mixture of -25+30 mesh and -30+35 mesh sizes.
The composition of the sintered abrasive grains, based on the
formulation used to make the grain, was, on a theoretical metal
oxide bases, for Example 8, 93% by weight Al.sub.2 O.sub.3, 4% by
weight ZrO.sub.2, 1.5% by weight SiO.sub.2, and 1.5% Fe.sub.2
O.sub.3, and, for Example 9, 90% by weight Al.sub.2 O.sub.3, 7% by
weight ZrO.sub.2, 1.5% by weight SiO.sub.2, and 1.5% by weight
Fe.sub.2 O.sub.3, based on the total metal oxide content of the
abrasive grain.
Examples 8 and 9, and Comparative Example E, belts were prepared as
described for Example 5, wherein the abrasive grain used for
Comparative Example E was the same as that used for Comparative
Example D. These belts were tested as described for Examples 5-7
and Comparative Example D except the infeed rates used were 127
micrometers (5 mils), 152.4 micrometer (6 mils), and 177.8
micrometer (7 mils). The results, which on one belt for each
in-feed rate (i.e., three belts were tested for each lot) are
summarized in Table 5 below, except the results for Comparative
Example E at an in-feed rate of 127 micrometers (5 mils) is an
average of two belts.
TABLE 5 Metal Removed at Metal Removed at Metal Removed at 127
micrometers 152.4 micrometer 177.8 micrometer Ex- (5 mils) infeed
(6 mils) infeed (7 mils) infeed ample rate, g rate, g rate, g 8
6667 6408 1577 9 8671 6338 4493 Com- 3784 1798 907 par- ative D
Example 10 and Comparative Example F
Example 10 was prepared as described for Example 1 except the
amount of ZRO was reduced by 46.4%, and the amount of AAMH was
increased by 7.8%. The composition of the sintered abrasive grain
was 89.5% by weight Al.sub.2 O.sub.3, 7.5% by weight ZrO.sub.2,
1.5% by weight SiO.sub.2, and 1.5% by weight Fe.sub.2 O.sub.3,
based on the metal oxide content of the abrasive grain.
Comparative Example F was prepared as described for Example 1
except no CS1 was used, the amount of ZRO was reduced by 46.4%, and
the amount of AAMH was increased by 9.6%. The composition of the
sintered abrasive grain was 91% by weight Al.sub.2 O.sub.3, 7.5% by
weight ZrO.sub.2, and 1.5% by weight Fe.sub.2 O.sub.3, based on the
metal oxide content of the abrasive grain.
Example 10 and Comparative Example F were tested as described for
Example 1 except the abrasive grain used to make the coated
abrasive discs were graded into a 1:1 mixture of -25+30 mesh and
-30+35 mesh sizes, the load during the test was 7.73 kilograms (17
lbs.), and three discs for each example were tested. The average
total cut for Example 10 and Comparative Example F were 1353 grams
and 1230 grams, respectively.
Example 12
Example 12 abrasive grain was prepared as described for Example 1
except the silica sol was CS2, the calcined grain was impregnated
with MGN. Each 100 grams of calcined precursor was mixed with 30
grams of MGN which was prior to the impregnation was diluted to 60
ml. The impregnated grain was dried and re-calcined, the sintering
kiln rotated at about 2 rpm to provide a residence time in the tube
of about 15 minutes, and the sintering temperature was about
1375.degree. C. The composition of the sintered abrasive grain,
based on the formulation used to make the grain, was, on a
theoretical metal oxide basis, 93.5% by weight Al.sub.2 O.sub.3, 1%
by weight ZrO.sub.2, 3% by weight MgO, 1% by weight SiO.sub.2, and
1.5% by weight Fe.sub.2 O.sub.3, based on the total metal oxide
content of the sintered abrasive grain.
The sintered alpha alumina-based ceramic abrasive grain was
incorporated into coated abrasive discs as described for Example 1,
except the abrasive grain was graded to a 1:1 mix of -35+40 and
-40+45 mesh fractions (U.S.A. Standard Testing Sieves).
Comparative Example G
Comparative Example G coated abrasive discs were prepared as
described for Example 12 except (a) there was no ZRN or CS2 were
used, (b) the amount of MGN was increased by 50%, (c) the amount of
AAMH was decreased by 0.5%, and (d) the abrasive grain was sintered
at 1350.degree. C. The composition of the sintered abrasive grain,
based on the formulation used to make the grain, was, on a
theoretical metal oxide basis, 94% by weight Al.sub.2 O.sub.3, 4.5%
by weight MgO, and 1.5% by eight Fe.sub.2 O.sub.3, based on the
total metal oxide content of the sintered abrasive grain.
Example 13
Example 13 coated abrasive discs were prepared as described for
Example 12 except (a) the amount of ZRN was increased by 600%, and
(b) the amount of AAMH was decreased by 6.4%. The composition of
the sintered abrasive grain, based on the formulation used to make
the grain, was, on a theoretical metal oxide basis, 87.5% by weight
Al.sub.2 O.sub.3, by weight 7% by weight ZrO.sub.2, 3% by weight
MgO, 1% by weight SiO.sub.2, and 1.5% by weight Fe.sub.2 O.sub.3,
based on the total metal oxide content of the sintered abrasive
grain.
Example 14
Example 14 coated abrasive discs were prepared as described for
Example 12 except (a) the amount of MGN was increased by 133%, and
(b) the amount of AAMH was decreased by 5.3%. The composition of
the sintered abrasive grain, based on the formulation used to make
the grain, was, on a theoretical metal oxide basis, 88.5% by weight
Al.sub.2 O.sub.3, 1% by weight ZrO.sub.2, 7% by weight MgO, 1% by
weight SiO.sub.2, and 1.5% by weight Fe.sub.2 O.sub.3, based on the
total metal oxide content of the sintered abrasive grain.
Example 15
Example 15 coated abrasive discs were prepared as described for
Example 12 except (a) the amount of ZRN was increased by 600%, (b)
the amount of MGN was increased by 133%, and (c) the amount of AAMH
was decreased by 10.7%. The composition of the sintered abrasive
grain, based on the formulation used to make the grain, was, on a
theoretical metal oxide basis, 83.5% by weight Al.sub.2 O.sub.3, 7%
by weight ZrO.sub.2, 7% by weight MgO, 1% by weight SiO.sub.2, and
1.5% by weight Fe.sub.2 O.sub.3, based on the total metal oxide
content of the sintered abrasive grain.
Example 16
Example 16 coated abrasive discs were prepared as described for
Example 12 except (a) the amount of CS2 was increased by 200% and
(b) the amount of AAMH was decreased by 2.1%. The composition of
the sintered abrasive grain, based on the formulation used to make
the grain, was, on a theoretical metal oxide basis, 91.5% by weight
Al.sub.2 O.sub.3, 1% by weight ZrO.sub.2, 3% by weight MgO, 3% by
weight SiO.sub.2, and 1.5% by weight Fe.sub.2 O.sub.3, based on the
total metal oxide content of the sintered abrasive grain.
Example 17
Example 17 coated abrasive discs were prepared as described for
Example 12 except (a) the amount of ZRN was increased by 600%, (b)
the amount of CS2 was increased by 200%, and (c) the amount of AAMH
was decreased by 8.6%. The composition of the sintered abrasive
grain, based on the formulation used to make the grain, was, on a
theoretical metal oxide basis, 85.5% by weight Al.sub.2 O.sub.3, 7%
by weight ZrO.sub.2, 3% by weight MgO, 3% by weight SiO.sub.2, and
1.5% by weight Fe.sub.2 O.sub.3, based on the total metal oxide
content of the sintered abrasive grain.
Example 18
Example 18 coated abrasive discs were prepared as described for
Example 12 except (a) the amount of CS2 was increased by 200%, (b)
the amount of MGN was increased by 133%, and (c) the amount of AAMH
was decreased by 6.4%. The composition of the sintered abrasive
grain, based on the formulation used to make the grain, was, on a
theoretical metal oxide basis, 87.5% by weight Al.sub.2 O.sub.3, 1%
by weight ZrO.sub.2, 7% by weight MgO, 3% by weight SiO.sub.2, and
1.5% by weight Fe.sub.2 O.sub.3, based on the total metal oxide
content of the sintered abrasive grain.
Example 19
Example 19 coated abrasive discs were prepared as described for
Example 12 except (a) the amount of ZRN was increased by 600%, (b)
the amount of MGN was increased by 133%, (c) the amount of CS2 was
increased by 200%, and (d) the amount of AAMH was decreased by
12.8%. The composition of the sintered abrasive grain, based on the
formulation used to make the grain, was, on a theoretical metal
oxide basis, 81.5% weight Al.sub.2 O.sub.3, 7% by weight ZrO.sub.2,
7% by weight MgO, 3% by weight SiO.sub.2, and 1.5% by weight
Fe.sub.2 O.sub.3, based on the total metal oxide content of the
sintered abrasive grain.
Grinding Performance Evaluation of Examples 12-19 and Comparative
Examples G
The grinding performance of Examples 12-19 and Comparative Example
G coated abrasive discs were evaluated as described for Examples
1-4 and Comparative Example A, except the workpieces were 4150
steel workpieces, and the load was 7.7 kilograms. average total cut
for each example is reported below in Table 6.
TABLE 6 Example Total Cut, grams % of Comp. G, % 12 792 110 13 725
101 14 790 110 15 830 115 16 711 99 17 700 97 18 728 101 19 702 98
Comp. G 721 100
The grinding performance of Examples 12-19 and Comparative Example
G coated abrasive discs were also evaluated using the same grinding
test described for the results reported in Table 6, except the load
was 5.9 kilograms. Two discs were tested for each example each. The
average total cut for each example is reported below in Table
7.
TABLE 7 Example Total Cut, grams % of Comp. G, % 12 713 120 13 631
106 14 660 116 15 709 119 16 664 111 17 673 113 18 351 59 19 663
111 Comp. G 596 100
The grinding performance of Examples 12, 15, and 16 and Comparative
Example G coated abrasive discs were also evaluated using the same
grinding test described for the results reported in Table 7, except
the fifteen one minute intervals were used instead of ten
one-minute intervals. Two discs were tested for each example. The
average total cut for each example is reported below in Table
8.
TABLE 8 Example Total Cut, grams % of Comp. G, % Comp. G 794 100 12
907 114 15 931 117 16 983 124
The grinding performance of Examples 12, 14, and 15 and Comparative
Example G caoted abrasive discs were also evaluated using the same
grinding test described for the results reported in Table 6, except
the workpieces were 1018 mild steel. Two discs were tested for each
example. The average total cut for each example is reported below
in Table 9.
TABLE 9 Example Total Cut, grams % of Comp. G Comp. G 796 100 12
1076 135 14 1251 157 15 1066 134
Various modifications and alterations of this invention will become
apparent to those skilled in the art without departing from the
scope and spirit of this invention, and it should be understood
that this invention is not to be unduly limited to the illustrative
ebodiments set forth herein.
* * * * *